The easiest way is to just install umbrel from Github (instructions on the README) onto your Linux PC (or a VM with linux that you give almost 100% of your host PC’s resources)
Then once everything is synced, set up umbrel on the pi and start syncing. Wait a couple minutes til you start seeing the % go up from 0, then shut down the pi and remove the SSD.
Connect the SSD to the PC, stop the local installed umbrel using
sudo ./scripts/stop as per the instructions and send over the files from the installed Umbrel to the pi’s SSD. (You don’t want to copy over bitcoin files if the source or target are currently syncing. So make sure everything bitcoin related is not running.)
The folders you want to copy are:
Once you’ve copied those over to the SSD in the proper location (you can delete the existing ones and replace them with the synced ones.) Plug it back into the pi, and start up Umbrel, it should take a while the first time booting, but it should be 100% (or close, depending on how long it takes you to copy over the files) as soon as you log in.