I've been a paid subscriber of Evernote since 2015 and in recent years have experienced significant disruption, wasted time, and loss of data as a result of Evernote's failings and questionable decisions. EN is currently v10.56.9 on my Mac. Having read several threads it is clear that many others are struggling with the viability of EN. This reply is just intended to share my experience and opinions.
These are the main problems that I've encountered (in the past, and currently) :
Notes have been duplicated, triplicated, and quadruplicated even as I have been working on them (i.e. in real-time as I was creating / editing a Note). At first I thought this was a glitch and that each dup/trip/quad-licate was an incremental 'save', but it quickly became apparent that the data was not being saved incrementally. For example a piece of text was included in Note v1 and v3, but not Note v2 and v4. It was bizarre.
Notes have been lost. I speak with my accountant at least once per month and many of those discussions require me to take notes. There's a gap of ~18 months in the relevant Notebook where there aren't any Notes, and it is inconceivable that I wouldn't have created any Notes during that timeframe. EN Technical Help has requested the precise title of each Note - this isn't practicable, because I don't have a photographic memory. I've suggested a potential partial title of a Note, based on the date of a scheduled Zoom call in my calendar, but EN has not responded.
I've looked in the suggested Library locations (I know how to display Hidden Folders), and have searched, but there doesn't seem to be a database or any folders/files with anything significant in terms of data content.
I do not recall when EN migrated from 'local data, Cloud synchronised' to 'Cloud data, temporary cached local data' but it seems that my Time Machine backups do not go back to a time when I was using the previous release of EN i.e. prior to v10. I have resigned myself to the acceptance that I do not have a local copy of the Notes which have been lost.
In hindsight it seems clear that I should have done more research so as to fully understand the fundamental changes in EN v10, rather than being herded along the "look ! new ! shiny !" upgrade path. I regret not holding-off for much longer.
Far from being a productivity-enhancing App EN has now, unfortunately, become quite the opposite for me. Permanent loss of data by a service provider is unforgivable. Removal of local data for backup purposes is unacceptable. EN annual subscription charges have become very uncompetitive.
So now I'm on the hunt for a workable alternative, but I haven't found a Notes App which ticks all my boxes. I may even stop using Notebook/Note Apps altogether and simply use documents, in a logical folder structure, real-time synchronised across my devices via Dropbox. My DB subscription includes a rolling year of searchable version backups, which would provide an extra layer of information recovery if I ever needed it. I'd lose some useful functionality, and I accept that it would probably represent a big backwards step in terms of modern technology and processes, but at least it would be reliable and timeless (i.e. not subject to enforced changes to workflow and data storage strategy/platform from Apps providers) and I wouldn't be forced to use proprietary technologies which can prove to be so imprisoning of the customer.