Agree, the pi is way too low power to handle nextcloud comfortably. In the same price range, it's much better to buy a used NUC (even with a celeron!) compared to the beefiest Raspberry Pi 4 out there.
TBF I think this says more about Nextcloud than the Raspberry Pi. I also suspect it can be helped with some setup - I imagine the difference between disk I/O performance is going to be greater than the CPU differences if you're comparing a Pi4 to a recent-ish PC.
