And that won’t be something that changes with the tighter control over App permissions. Newer versions of Android and iOS are much stricter about background location access, even if AppSheet added a way to ping the location automatically every few minutes.
As a potential help though, AppSheet supports NFC. You could have an NFC tag at a Check-In/Check-Out station somewhere that the users scan with the app triggering to record the times. It’s a great idea as it works double duty as reinforcing that they physically have to be there in order to Check-In/Check-Out and it doesn’t have to involve GPS at all.