Similarly, a local-first (PouchDB) budgeting app I built[1] went open source[2][3] a few years ago. It's worked out well, I love seeing what everyone does with it in their forks. Unlike Actual however, I maintain a paid subscription service while being open source.
It's worked out quite well. Luckily it's not a huge time commitment as a side project, probably due to no native apps. I've also shifted from active development to maintenance, with sporadic updates every now and then. For example, I recently moved everything from Gitlab to Github[4] and upgraded a bunch of dependencies under the hood to get everything compiling on Apple Silicon. (For example, I now run AngularJS tests with Jest, hehe.)
[2] https://github.com/financier-io/
[3] https://blog.financier.io/financier-is-now-open-source-bdfe9...
[4] https://blog.financier.io/weve-moved-to-github-4617239b9fa3