QB64 needs a couple of things to change the IDE font:
First, it has to find your font to start with. Make certain you paste the whole path to the font you're wanting to use. (Windows is easy as they have a default font folder. I don't know where Linux stores them)
Second, make certain it's a MONOSPACED font. You can't use one that isn't. (Courier New is often a good choice.)
With those two things in place, the IDE should change size to what you desired and save the value for you forever more.
If all else fails due to file/security/user permissions or such, try copying the font you want directly into the qb64pe folder with the executable. It might save you a few issues.
First, it has to find your font to start with. Make certain you paste the whole path to the font you're wanting to use. (Windows is easy as they have a default font folder. I don't know where Linux stores them)
Second, make certain it's a MONOSPACED font. You can't use one that isn't. (Courier New is often a good choice.)
With those two things in place, the IDE should change size to what you desired and save the value for you forever more.
If all else fails due to file/security/user permissions or such, try copying the font you want directly into the qb64pe folder with the executable. It might save you a few issues.