Not intended to be user-editable... but you can carefully edit the preference file (Mac) or registry (Windows) to get rid of these entries.
Since you're on a Mac, you'll find the preference file that you want in your ~/Library/Preferences folder
The name depends on the international release, but for the the US version of 14 at the moment, it is: com.graphisoft.AC 14.0.0 USA v1.plist
There is a key group called "Recent Documents". If you edit this, you must make the value of Project Number match the number of entries that you leave, and as you delete anything, you may need to renumber the "Project_n" entries.
There is a similar group of entries for any recent gsm objects that were opened.
There is a key called "RecentPlans" that sets the max number of entries that will be left in the recent project list. You might alternatively want to just set that to 4 or something low to purge the old entries and keep the list from growing in the future.
Personally, I'd recommend leaving it alone unless it seriously bugs you.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB