Question mark in a square symbol appearing instead of readable characters in Steam

I just came back on to Steam on 10/11/2025 to try and play “Sid Meier’s Civilization VI” which I purchased a few years ago. However, when I logged into Steam, the fields for user name and password I typed show a question mark in a square instead of the actual characters I typed.

Although it still accepts what I typed and logs me in, most (if not all) of the text in many areas of the screen have the same “question mark in a square” character instead of legible characters. 

I am running on an M4 iMac, running MacOS 15.7.1 with 24 GB of RAM. My Mac’s “FontBook” appears to have all the fonts that were on the previous 2019 Intel Mac that I migrated from. I think Steam uses the “Arial” font and I still have that in the Font Book. My Steam Client appears to be up-to-date.

Has anyone else experienced this problem? Is there a fix?

I’d appreciate any useful suggestions. (Although I’m not sure if I’ll be able to read them. They may come out as question marks in a squares!)

Thanks for your help.