Accidentally ran sudo fstrim -av at Dom0


today was my first day with QubesOS and Linux in general. So I wanted to update the TemplateVM according to the manual at In-place upgrade of Fedora TemplateVMs | Qubes OS
Unfortunately I messed up at step 5 and ran $ sudo fstrim -av at Dom0 instead of fedora-33.

Question is: Have I messed up my system beyond repair (memory management) or can I still transfer my personal files to my new Qubes device? This may be a dumb question.

You should be totally fine. This command just tells the underlying system that some sectors are not used anymore and can be recycled.