I track my app usage with usageDirect. It displays the usage time of all apps and compiles the data into several graphs.

The best app for limiting apps I found is TimeLimit.io. You can use it for your own device, but it also supports limiting and controlling other devices, e.g. your children’s.

Both apps can be found on F-Droid.

There is (Open)TimeLimit, which is originally an alternative to FamilyLink, but you can set up very specific limits in it (with experimental support for per-activity limits).

Edit: dang, I haven’t read the other answer completly, they also recommend TimeLimit, my bad