SQLite works well for app files. Bentley uses it for all sorts of stuff and I had way fewer corrupt files in their format than Autodesks. :)

Do note that sqlite itself doesn't have the kindest handling of date/times, you are at the mercy of your data provider (unless you are going native) Especially when timezones are involved.

If it's running on windows machines you could consider Sql Server LocalDB (runs in user mode, i believe you are allowed to distribute as such in an app). But it doesn't sound like that would make sense from what I've read for your case and tech stack.

Sqlite is a good start because even if you are wrong, it should be pretty dang easy to migrate to whatever is right. :)