Great, thanks for the info.
I found this tutorial for installing TWRP on OP 3T. So I could easily get back to my current state by this.

@AppLee this is why I said it "gives you the feeling of".
Yea I'm going to keep it enabled. Thanks for your support.

Because I'm short in time I will keep my OnePlus One as main phone for the moment. Never change a running system.
When I got time or the OP1 will stop working I will give the OP 3T a try.
Thanks for your feedback. I really really enjoy this great OS as it is growing to be a really great alternative to Android for me.

Never mind, I would just like to get the answer to my last question as this is still bothering me.

Thanks for highjacking my post by the way.
I guess my thread is finished when my initial questions are answered?

Is it possible to install UBports in an Multirom enviroment on the OP 3T?
-> No

How could I restore TWRP if I would like to switch back to an Android ROM?
-> Basic TWRP installation tutorial works

If I understand this correctly i have to install gst-droid to use the camera. But it says that "by installing packages via ubports-qa or apt, you should not install system updates via the system settings app anymore". Does "sudo apt update and sudo apt upgrade" also upgrade apps from the OpenStore? And is it still possible to install apps from OpenStore afterwards?
-> ???

Great, thanks for the info.
I found this tutorial for installing TWRP on OP 3T. So I could easily get back to my current state by this.

Hello Forum,
I'm currently using an OnePlus One but I'm thinking about upgrading to the 3T I have bought recently.
Is it possible to install UBports in an Multirom enviroment on the OP 3T?
And if not: How could I restore TWRP if I would like to switch back to an Android ROM?
If I understand this correctly i have to install gst-droid to use the camera. But it says that "by installing packages via ubports-qa or apt, you should not install system updates via the system settings app anymore". Does "sudo apt update and sudo apt upgrade" also upgrade apps from the OpenStore? And is it still possible to install apps from OpenStore afterwards?
Thanks for your feedback.

@AppLee this is why I said it "gives you the feeling of".
Yea I'm going to keep it enabled. Thanks for your support.

I'm used to this from using Android. It gives you the feeling of having control of your data. haha
Maybe I should just keep it enabled all the time.
Thanks for your quick feedback.

@AppLee Yea you right, first localization is slow. After this GPS is okay.
What exactly do you mean by "first fix". So after each reboot or power on the phone has to relocate itself for the first time? What about turning GPS off/on in the settings?
Thanks for clarification, I'm using Photon as well, and its suggestions are reasonable.

@Lakotaubp with GPS always enabled and the phone was powered on for some time I guess? 20s sounds great.

Thanks for your support. It has been a while and I still enjoy my UBports phone.
BUT the main problem still remains with the slow GPS. If im on the go and need some directions I cant wait for 10 minutes and/or reboot the phone until it works. This is a great practice to keep calme though.
Searching streets in Germany works better now. I switched the maps once but I cant tell whats selected right now. It only says "Mapbox (Voreinstellung)" in maps settings menu. But I cant tell if it is selected.
@AppLee how can I see the selected search engine?
I just bought an OnePlus 3T, will the GPS be as slow as with my OP One using UBports?
Greetings.

@AppLee Pure Maps does not give me any suggestions at the moment sadly. It neither finds any German city at all. I don't know whats wrong with it. Even tough I can zoom into cities and streets successfully.