I’ve said this before, but I need to keep repeating it based on the number of queries I get. nvALT is at end of life, unless someone picks up the reigns and modernizes the (open source) code base. As it stands now, nvALT barely functions on modern OSs.
I started using nvALT years ago. Brett is correct, you should extract the notes as Markdown files at least. I don’t know what you’ll lose if you were also using rich text format in that database.
I have been beta testing nvUltra which looks quite nice. However, since it’s not released and future development looks uncertain, and also I sometimes need to work with Windows machines, I’m mostly using Obsidian these days. It has lots of features and plugins, and you can use it in an IDE or Visual Studio Code type of way, splitting windows, etc. It also has a similar concept of vaults as nvUltra.
The downside may be for instance that it can be a bit complex, at least regarding user interface. And especially in the mobile app. But at least it has a mobile app I guess. And using nvUltra and Obsidian on the same folder of Markdown files seemed to work quite well, even with a folder structure, though of course there are some parts where it’s not totally compatible.
Then the Bear app has a great user interface with Markdown notes, both on Mac and on iOS. However, the downside is that it stores the notes in its own database. This was too much for me to use it, at least for work. You can’t open a note in external application, backup notes, put the notes in Git, version them and so on. And it’s only Mac ecosystem. They made a recent post where they said they may create a Panda application that works similarly with local Markdown notes, though.