I ran into the same issue with the M1 processor. Still unsure if it is a Cryptomator specific issue with Webdav or if it is a Webdav issue in general. If it’s the latter and anyone has found a fix, would love to hear about it since I use Webdav for other stuff.
Now regardless if Webdav is fixed for M1 or not, or even if you’re in an Intel machine, I really recommend everyone to use MacFuse instead of Webdav, is so much faster and reliable than Webdav which is why I’m guessing Veracrypt/Truecrypt have been using it for the longest time.