1) why cant your new phone use the authenticator?

2) does the authenticator work on your old device

3) have you followed the process of moving your authtenticator

https://help.steampowered.com/en/faqs/view/29A9-9EEE-09F0-75F9

4) Do you have the R-code for your authenticator, as you can, worse case, remove your authenticator from your old device and then add it new on the new device. This does result in a longer trading cooldown though so following the process in #3 makes the cooldown LESS (Its like 3 days I believe vs like 7-15 days)

I cant Move it because i get an error that i cant at this Moment and i should try again. And i cant find my Old device nor am i sure that the Steam App is still Installed and i wrote a Steam Support ticket today

... oh, you already contacted Steam Support.

I used to forget to de-/un-authenticate my Steam Authenticator, but was always able to 'reset' and access my account by using a different method. I have my phone number stored/linked to my Steam account.

Now, if I ever forget or switch mobile devices, I can always use my phone as a legit authentication method before re-installing the authenticator (or installing Steam on mobile).

I tried that but it asked for my Steam Guard Code and guess what i dont have correct this code i guess i deleted it accidentally or never received one 🥲