Outlook MacOs does not ask for passwort, smtp/imap server when adding custom email - why?

Ive do not have a mac only linux and do not use outlook personally but ive set up as the web dev the mail for my client and she asked me to remote connect her mail since its not working and maybe i see something she does not, iam just the first contact person helping out of kindness. I did believe that microsoft would never give any screen sharing support even if its just 2 minutes.

But in end ive tried the same things she did.

Ive tried adding contact@johndoe.com
It automatically was added, i have no clue why outlook did that. Without asking for the password or telling me „this is not a outlook mail this is a ionos strato hostinger etc mail server behind, please tell us where“

Of course this could not work, and then she tole me about outlook legacy, so we switched to legacy and there you could enter your details when adding an account, ive tried it again entering 993 465 etc. copy pastet everything 100% correct. It said no does not work and then i couldnt help either since i do not know enough about outlook, but wanted to make sure everything was entered correctly.

Adding this email to thunderbird, ios or web client etc everything worked.

From what i know it should work with Outlook New and there should never be a need for a Legacy version. Microsoft cannot be that horrible but these companies try to sync useless stuff. Maybe someone can screenrecord that for me or screenshot and blur his information and show me what to do?

What happened there in the background?
Why does it not ask for the passwort and fake „connects“ automatically.

Would be smart to first get new solutions from you before trying new ways.

She does want to have everything in outlook, she has one seperate outlook i think and 2 other services like yahoo google or something and the custom mail on her webhosting.

If nothing works its probably easier to connect everything to macos mail or thunderbird but ive want to try solving this issue.