I would perform a clean install by first erasing the whole physical drive before installing macOS again. When you migrate, just migrate your user account(s). Manually reinstall your third party apps. It is possible you have some apps that are not compatible with the new OS.
https://support.apple.com/guide/disk-utility/erase-and-reformat-a-storage-device-dskutl14079/mac
Those instructions are for an Intel Mac. If you have an new M1 Apple Silicon Mac, then those instructions I just linked may not be applicable to the M1 Mac.
Were you transferring over WiFi? This will be extremely slow. It would be better to transfer over a wired Ethernet connection. You can also put the old Mac into Target Disk Mode so you can use a USB3 or Thunderbolt cable to connect it to your new Mac for a faster more reliable connection. TDM makes the old Mac appear as an external hard drive with the added advantage of not having an OS running on the old Mac which may be slowing things down as well.
Or migrate from your backup.
Or the hard drive on your old Mac may be starting to fail. I would check the health of the hard drive on the old Mac by running DriveDx and posting the report here using the "Additional Text" icon which looks like a piece of paper.
I highly recommend you have frequent and regular backups. It is impossible to recover accidentally deleted data from an SSD plus an SSD can fail at any time without any warning signs. Also if the Mac has a hardware issue it will likely be nearly impossible to recover data from the SSD except perhaps using an expensive professional data recovery service.