I sent mine back last week, same situation as you, purchased a new one to replace old one that support was ending on… nobody could fix the time machine issue for me so I sent it back - Im still waiting for my refund though!!
I tried all of their troubleshooting tips etc , technical support via email but nothing worked so sent it back for a refund - seems to be a massive issue… what OS are you using?.. Im on Monterey - think they need to stop selling them until this issue is fixed - Im proper gated though as i had my old mycloud for many years with no issues at all - purchase a mycloud home via the replacement scheme and boom there goes my way of doing TM backups… not sure where to go in terms of devices for TM now as Ideally I want something similar to cloud so i don’t have to continuously have my devices all plugged in.