I had exactly the same issue a few hours ago on my Xubuntu 24.04.2 laptop.
I’ve tried several troubleshooting actions.
Eventually, this one worked for me and snap-store just came back to normal:
sudo snap-store --quit
sudo killall snap-store
sudo snap remove snap-store
Reboot the device, then:
sudo snap install snap-store
I don’t know what happened, it seems this issue followed a system update I received yesterday. (some libgtk-4 packages). So maybe something went wrong with those packages being updated.
But anyway, this should also work for you 