PinkElephant

The versions working with iOS 12 (and older) have been discontinued.
It may be you can still download the client, but it will never again connect with the server. The interface for the legacy clients has been closed on the 23rd of March.

You need to switch the browser to desktop mode on mobile devices. Then try again.
I found it unusable on phones, and quite ok on tablets.

https://support.apple.com/en-en/guide/iphone/iph8903c3ee6/ios
As already advised several times:
Uninstall the Evernote app.
Do a forced restart - this is not a normal restart of the iPhone. See the support article how to do it, or search the internet to find the advise in your language.
After the iPhone is on again, download the app, open, log in.
Install the widgets on the iPhone Home Screen.

Yes, the limit was lowered to Android 9 about a year ago.
Good for owners of older devices.
But Android 6 is too old, sorry. Check if you can upgrade to at least Android 9. Else you can try to use the web client - the browser on the tablet must be set to "Desktop Mode" to allow for it.

Just pulled out my venerable iPad Air 2 to give EN a try there. It pulled the update to EN 10.83. on opening it took a while telling me it needs to bring the database structure up to date.
At the moment it is syncing. In general it is quite slow now, no comparison to running EN on my iPad Air 5 (with M1 processor).
One observation: The Air 2 should be able to run iOS 15.7. For security reasons it should not be kept with iOS 13. From my experience taking it to 15.7 will not make it slower.

If another app is used for the edits, I think the sandboxing concept of both mobile OSes will prevent it to save itself back. Sandboxing means that each app receives its own adhere of memory where it is allowed to execute. An app is not allowed to write by itself into the sandbox (memory range) of another app. This concept provides for security - but makes it difficult for data to flow between apps.
Data flow between apps is done through the user deciding to share it to another app.
EN can open the spreadsheet app and send it the file for editing. But the spreadsheet app can’t send it back to the note.

You need to run on Android 9 as minimum system requirement. When below it will only offer the v8 client. This client does not sync any more.
You need to update the tablet to Android 9 to be able to install the current version 10 client.
Your subscription date has nothing to do with the software version your tablet can execute. This only depends on it’s operating system.

The usual advise was: In the evening, turn off the auto-lockscreen, put the device on charger, place the EN app as active app in the foreground, and let it run through the night.
Plus avoid „download all“ for the initial download. But that’s not the case here.
Since some releases (maybe 10.70) offline download was improved a lot, and is much faster. All this from iOS, no experience with Android.

What is the count when you open the web client ?
If it is again the Pixel that is off, uninstall the app, dump all data when asked. Restart the phone. Install the app again, log in, and keep it open while it downloads the notes and metadata.

Web Clips are a static download. They are stored as they were when clipped.
The only connection to the original website is the URL saved in the note. You can visit the site again - which will show the current site. But this doesn’t change the clipped copy.
Example: A page is clipped when it showed freely. Later it is moved behind a paywall.
The clip will still show as it was - the URL will be redirected to a login page.

There is only 1 default notebook for the whole app.
On some tools like the Web Clipper you can set another notebook, but not inside of the main app.

Send your wish to turn it off to Support, or at Feedback.
https://help.evernote.com/hc/en-us/requests/new   feedback@evernote.com

Empty the trash. Notes in the trash count into the limit.
Avoid to have more than 1 notebook. If you have more, it locks new note creation as well.

There never was such an extension. The only browser allowed on iOS was Safari / WebKit. Extensions were introduced with iOS 16. Up to now the WebClipper extension has not been ported from the Mac to work on iOS.
I don’t remember that there ever was an option to create new tags in the iOS sharing dialogue. Since it sends the data into the local client, the options it can use are limited. On iOS all apps run in their own sandbox.
The WebClipper doesn’t use the local client, it works through the API directly on the server.

This is a MacOS function, has nothing to do with EN:
Open MacOS settings (pictures taken with Sonoma), choose keyboard (1), then Text Input, Sources, Edit (2):

 
This toggle (3) turn the conversion on and off:

 

Did you switch the browser to desktop mode ?
The web client is not supported on mobile browsers.

Web Clipper does open a Safari tab briefly, uses it for the login and shows a message when this was successful.
First make sure you run the latest software. The client is 10.78 now, and a new web clipper was just released. You need to update web clipper in Safari extensions.
Then check in web clipper settings if „auto filing“ is enabled.

As said the Forum is driven by an independent provider contracted by EN to run this place. They have their own support and forum:
https://invisioncommunity.com
EN support is here, but expect quite a long reaction time.
https://help.evernote.com/hc/en-us/requests/new  

On which client ? I see this in a side panel (1), and the text (2) tells me to draw a widget to the place where I want it to show.

1) The link is as official as it gets. You could use filehippo.com as well.
2) Nobody knows. What we know that in offline mode there must be an existing prior login to allow any offline access. Logging out before going offline results in not being able to open the account through the client.
The only way to be sure is to find out. And if not, you should better have a Plan B.

In v10 you have several options: You can move the database to another path, even an external drive (should be a SSD), which however is not recommended. You can even skip having a local database altogether. If you have a fast enough internet connection, this is a possibility that didn't exist in prior versions.
Or you simply go with the web client - it is pretty close to the installed client.

Minimum system requirements.
Instead of asking you could simply check in the help database yourself. What you get there is official.

@Boot17 I think for the file link to work, if must be 3 slashes ?
evernote:///URL

Download the most recent version from the EN website, install it.
It is v10.75 or v10.76 already. Versions below 10.60 (or close) are no longer supported, as are all legacy versions.
If the installation doesn't work out, uninstall USING REVO UNINSTALLER. Then restart the PC, and install again.

Windows server is not a client software. You may have reasons to run it, but EN is not prepared to be installed as server software.
It asks for Windows 10 as minimum system requirement.
Probably installing Win 10 in a VM, and then installing EN into the VM is one way around. Or use the web client.