Inkscape installation issue on iMac

Either the font cache data on your Mac is corrupt, or you have a third party font conflicting with the one that's supposed to display there.

To clear the font cache, close all apps you currently have open.

Launch Terminal and copy/paste this command in:

atsutil databases -removeUser

If it asks, enter your admin password to complete the action.

Immediately restart the Mac.

Test Inkscape to see if that fixes the issue.

You are two Sonoma updates behind. You should have v14.7.1 installed and that may or may not have a bearing on Inkscape v1.4. The process of updating to Sonoma 14.7.1 will also rebuild your font cache and clear out the current System cache, so that may be a good thing.

Your Software Update may now show Sequoia v15.1 but if you scroll down, you will see a link named another update is available which offers the Sonoma 14.7.1 and potentially Safari 18.1 updates. This will not upgrade you to Sequoia.

I installed Inkscape v1.4 on Monterey (Intel), Ventura (13.7.1), and Sequoia v15.1 without any of the issues that you have shown.

You might want to ask on the Inkscape Forums as well.