Hello!
I have just installed GrapheneOS on a Pixel 7 (got it specially for this reason).
Some of the default apps didn't feel quite right and I also needed a calendar, voice recorder and notes app.
You can checkout simplemobiletools. Besides of Google Play you can also find them on F-Droid or you can get the APK on their's website.
The apps are working just fine for me. Imagine a simple, bloatless calendar app that's not spying you in 2023.
Review from Kenny (Mental Outlaw) can also be found here:
https://www.youtube.com/watch?v=SO3porIQ8_8