v2026.2.0-latest +1 seems to have introduced (at least for my installs) that mobile rendering only shows threads and content on half (left half) of the screen when foldable is “wide”
Header, footer, and column headers (“topic replies, views activity”) are all full width
I can understand that you don’t want to share your forum publicly. Maybe you can find another forum with the same problem on https://discover.discourse.com/ and share that.
You can also try the different themes here on Meta and on try.discourse.org. Though, since safe mode didn’t help, it doesn’t seem that likely it will help.
Perhaps that is the change that caused the problem. Is that within the week between your updates?
The issue you’re seeing is caused by a conflict between the new viewport-based style and the old mobile view. It looks like the Viewport based mobile mode site setting is currently disabled in your admin.
To fix this, simply enable the setting under your site settings. This should resolve the layout conflict.