Messages font size not working

I would like to adjust the font size of my Messages on new Mac Mini, but the CMD + and CMD - keys are doing nothing at all. I've also tried going through the View menu to "Make text bigger" and again, there is effect. The key combinations work for other apps, so it is something unique to Messages. Apparently one cannot uninstall and reinstall Messages, which normally I would do to fix something like this. I'm not going to change screen size to change the font of one app, since it needs to work as designed, so please don't suggest that. I've logged in and out of Messages, but no change. This has been going on a while, not sure when it started, and I hoped 13.5 would fix it, but no go. Any ideas?

Thanks.