Recommendations for a FOSS Cross-Platform Note-Taking Application

Up to now I've been using Simplenote, which has a Linux client (but also Android & iOS) & supports live collaboration on notes. However, Simplenote hasn't had a meaningful update for a long time, & it's recently been behaving strangely, e.g. notes undeleting themselves, line duplications & undeletions.

Can anyone recommend an alternative? Spinning up an ownCloud/nextcloud instance just to use Joplin feels a little overkill. I stumbled across turtl, but the project looks abandoned.