SRR
Hi SRR,
welcome to the great GOS!
Yes, there are so much possibilities to optimise the OS, but it can suddenly go wrong, if you switch something wrong…
Either you have stumbled across a bug in the theme settings or you have inadvertently changed something in the app settings that is better not to do.
For example, you switched off the "App start" authorisation for the app launcher.
Or deactivated an important app?
If you can remember, where you have made the last changes, then you might be able to undo it.
Go back into the settings menu to see all apps.
There you can tap on an app and then – if this app is e.g. disabled – you can enable it again.
Maybe you have changed the launcher app?
Then tap on it and check e.g. the setting of “Start App” down below. It must be “Yes”, if the original launcher app is your launcher app.
If you can't remember and no other member of this great forum has a remedy, then you can reset the app settings (but wait a few hours for better answers of other forum members!):
Go to settings, then down below to System, there down below on “Options to reset”.
Do not reset all!
Be careful, only select “Reset App Settings” here for this problem
(no factory reset, only the app settings!).
It's better to wait for further feedback from other members, because you may have made extensive settings to one or the other app that you haven't written down and then it would take a lot of time to set everything up again (design, backup paths for exporting data, etc.).