Hello deep-diver,
Thank you for using Apple Support Communities! I understand that GarageBand becomes unresponsive when opening the Media Browser on your Mac. I would be happy to help point you towards a resolution.
Let's start by confirming your Privacy settings for GarageBand. Open System Preferences > Security & Privacy, click the Privacy tab, then click Photos. Confirm that there is a check next to GarageBand in the list of apps with access to your photos. If the box is already checked, you may want to uncheck it, then select it again.
Open GarageBand and test if the behavior persists. Let us know the results.
Cheers!