Main problem facing any app that needs to run in the background is that Apple only allows it for certain use cases - VoIP, audio/airplay, location and BLE being the main ones. That's why since iOS 13 users have been seeing alerts that apps with no reason to need Bluetooth are requesting it.
So I deny most apps use of this, as it's clearly just a ploy to keep their app running when it shouldn't be. Something like the Termius app you cite has a legitimate reason to run in the background though and has to ask for one of those permissions.
It's a weird grey area IMO. I'm sure if you asked the Termius developers they may tell you that they don't even use the location data and that it's just a mechanism to keep the app running. However, the fact that we as users don't know this for sure is a problem that Apple could fix by adding a specific background permission alert.
So I deny most apps use of this, as it's clearly just a ploy to keep their app running when it shouldn't be. Something like the Termius app you cite has a legitimate reason to run in the background though and has to ask for one of those permissions.
It's a weird grey area IMO. I'm sure if you asked the Termius developers they may tell you that they don't even use the location data and that it's just a mechanism to keep the app running. However, the fact that we as users don't know this for sure is a problem that Apple could fix by adding a specific background permission alert.