Everything (except Mozilla Firefox) on MacStudio fails to connect to the internet

Since a couple of days nothing except Mozilla Firefox will connect to the internet.

• Mozilla Firefox works smoothless
• dropbox or any other app won't connect
• Safari says either "this connection is not private" or "Safari can't establish a secure connection"

Computer: MacStudio M2

OS: Ventura 13.6.7

The problem popped up since I tried to transfer some data from my Mac Studio to my brand new iPad.

However, Airdrop didn't work (every transfer failed after 20 %). When I tried to connect thy iPad via USB my MacStudio opened a window and told me that it needs to install some additional software (which I canceled).

BUT: That's not the problem that I'm trying to solve. It's MAYBE just the reason for my troubles. I want my MacStutio to smoothly connect to the internet again.

I glad about any ideas.

Best, Rai