Here is the feedback I received from Evernote support
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Thanks for reaching out to Evernote Customer Support. My name is Chipo, and I'm happy to assist you with your concern.I understand that you are experiencing an issue saving the note you frequently work on as the checkmark button becomes unresponsive that it does no action once pressed. I appreciate and thank you for all of the information you provided, and for your effort in the troubleshooting you did by reinstalling the Evernote app. I recognize this has not been the best for your situation, and I apologize for the inconvenience this brings you. I just wanted to let you know that our development team is aware of the performance issue and is working ceaselessly to improve the app. I can assure you we're working diligently to fix it as quickly as possible.As you have already reinstalled the app, which should temporarily solve the issue on your end, you may follow these steps to use Evernote Web on your iPhone as a workaround:
From Safari iOS, go to Welcome Back
On iOS: Before signing in, tap on the ‘Aa’ button on the left hand side of the URL field, and select Request desktop site (If you see "Request mobile site", then it indicates that you are already on the desktop site.
Then, sign in from the three lines menu at the top right, and access your notes
Thank you for your patience and understanding. Please feel free to reach out to us for an update, or if you have any other concerns. Stay safe!