Maybe it would make sense to replace control code abbriviations with symbols for these codes?

[carbon-starlight]

I tried using a custom encoding file to visually distinguish more bytes than supported by ASCII, but this column is almost unreadable due to control codes taking 2-3 characters. Maybe it would make sense to use single-glyph representations, like ␀ for NUL?

https://en.wikipedia.org/wiki/Control_Pictures

I however wasn't able to just paste them into the corresponding file: NULs showed as question marks for some reason.

BTW, it seems like ASCII OEM does not have most C0 control codes at all

[paxcut]

this was just added to ImHex a few days ago. Check out the latest nightly and there is a button next to the one used to turn the ASCII column on and off that can be used to add all non-printable chars to the ASCII column

[WerWolv]

If you download the latest nightly you will also generally not have any question marks anymore. It will take what it can from the selected font and fill out anything else using Unifont