Scoured the forum and haven't found a solution to this exact issue.
The font is normally it's readable but when using the inventory list option in Ender client or the combat UI it looks like the first 2 cropped screencaps in the attached pic.
It's the same way in Vanilla client too.
I asked my friend to show me his UI and his font looks like the third screencap, completely different.
Scoured all of the ingame settings and didn't see anything for changing the font used in menus.
It has nothing to do with the UI scaling either, it's still an unchanged blocky mess there too.