looks like i cant edit this but some fonts look to be missing as well from the xfce terminal font drop down in the preferences too

When you open terminal and select about does it say QT Terminal? If you want terminal to run the xfce4-terminal try this run exo-preferred-application and change the default terminal emulator under the Utilities tab. Hope that helps, QT terminal I found limited on fonts myself.

it was qtterminal not xfce4-terminal as expected, which also was not even installed oddly. i dont recall seeing anything in the release notes about this change but it may throw off many people.
xfce4-terminal works as expected, qtterminal does not and isn't an expected application. i think this is also a change from previous kali versions as well.

We've used qterminal as the default terminal in the XFCE desktop since we made the switch. I don't know if we called out specifically that it was, but it has been the case as we found it fit our wants and needs a lot better than xfce-terminal.

This issue is caused by an update in Qt5 library not by qterminal per se.
For now, the only way to fix this is by manually modifying the fontFamily parameter inside ~/.config/qterminal.org/qterminal.ini. Once you've changed that the dialog works again.
For example use "fontFamily=Hack"

One of the reasons Kali uses qterminal and FiraCode font is to support font ligatures.

Actually, I've found that removing the space from the name fixes this issue.

simply edit ~/.config/qterminal.org/qterminal.ini and set fontFamily=FiraCode

was going to also report and saw this plus a bunch of forum posts for the same

https://forums.kali.org/showthread.php?51025-Can-t-change-Terminal-font-and-size-in-new-update
https://forums.kali.org/showthread.php?50975-Unable-to-change-terminal-font-on-new-installation
https://forums.kali.org/showthread.php?50088-Terminal-font-and-size-will-not-change
https://forums.kali.org/showthread.php?50415-Can-t-change-Terminak-fon-or-font-size

im ok with firacode fonts but some might not be, wether is readability or something else and they may not see this issue. changing the ini is ok but the ui also doesnt list all fonts as a secondary issue

@harpistlaundry
Changing the fontname to FiraCode (without the space) fixes the issue and you can now change the font using the dialog.
The fix has been added to the package so it'll be updated soon.

Fixed with kali-themes 2020.4.1

You need to remove your local settings ~/.config/qterminal.org/qterminal.ini