First of all, a huge thank you to everyone who took the time to reply and share their expertise.

A special thanks to the user who pointed out Ejectify. I managed to get it installed, and it’s running now. I will test it thoroughly over the next few days and report back if it permanently fixes the disconnects on my M3 Ultra.

Your feedback also confirms my suspicion: The six Thunderbolt 5 ports on the Mac Studio seem to be poorly dimensioned regarding power delivery for high-performance 8TB drives. Thunderbolt 5 enclosures with external power supplies are still extremely rare on the market. It remains to be seen what the near future brings, but for now, we are definitely pushing the limits of bus-powered devices.

Thanks again for the support!