(optionally self-hosted, or completely offline, or on their server) TimeLimit.io should be mentioned.
is even on fdroid

limit what applications they can launch
what websites they can visit
how much screen time they spend in an app or category of apps
disable in app purchases
disable pop up advertisements in app
require approval from parent account for any app download (including free)
remove ability to delete apps or change specific settings

Google family link gives you controls over:

Android app activity and limits
Filters on Chrome, including custom black and whitelisting for websites
SafeSearch to remove sexually explicit and violet results in Google Search
Usage limits, including individual app limits
Google Play purchases, content restrictions, approval for app installs
Google Assistant app access and voice matching
Location tracking to find your child's device
Account info
Google Photo sharing
Google account sign in controls across new devices
Activity control such as web and YouTube history

source Seems like rather similar options to me?
But I have to admit to never having used either anyway.