Why do I suddenly need SSH?

[ic2]

After a couple of uninterrupted and working Pulls (the most recent interruption that costed us a few hours was the introduction  of app passwords, which I had to create twice again so far when it stopped working, thank you very much for this 'safety feature') , the latest surprise was the message:

The authenticity of host 'bitbucket.org can't be established. (etc)

After again a long time of trial and error entering obscure commands in obscure 1980 style command prompts, I got a working SSH key which was apparently the solution and vould again pull the changes of the solution of my colleague. Let's see how many times/days it works this time before the next error or issue....

Does anyone know why I got this? I changed nothing and my colleague didn't either.  What changed and why?

It would be really great if we could synchronize code without having to spend time every time solving unsolicited changes like this.