I'm presuming from your screenshot that you've tried Troubleshooting Mode and restarting your Macbook?

Issues with a weird looking font or missing glyphs can be caused by a problem with a specific font and you need to identify this font and fix this. You may find that this can be resolved by finding and removing duplicate fonts installed in the local ~/Library/Fonts folder, that are conflicting with standard system fonts.

You can check in Font Book for font issues like corrupted and duplicate fonts. Note that you should be careful about disabling "Allow pages to choose their own fonts, instead of your selections above" as this will cause issues with iconic fonts used by webpages to display small icons (you may see text labels instead of icons).

I'm presuming from your screenshot that you've tried Troubleshooting Mode and restarting your Macbook?

yup on both acccounts, no solution

Issues with a weird looking font or missing glyphs can be caused by a problem with a specific font and you need to identify this font and fix this. You may find that this can be resolved by finding and removing duplicate fonts installed in the local ~/Library/Fonts folder, that are conflicting with standard system fonts. You can check in Font Book for font issues like corrupted and duplicate fonts. Note that you should be careful about disabling "Allow pages to choose their own fonts, instead of your selections above" as this will cause issues with iconic fonts used by webpages to display small icons (you may see text labels instead of icons).

I checked for duplicates and there were none. I cannot be certain, but I first disabled and then uninstalled Better Display. I found that the issue didn't appear. Perhaps the 26.4 upgrade (which seemed substantial) broke something Better Display used. Anyway, now solved.