If all the channels are already forced closed by all your peers, you just have to wait until the sats will be available in your onchain wallet. Force closing can take longer time, be patient.
No need anymore for restoring the channels backup.
Just use your umbrel wallet seed into Bluewallet or Zap desktop to restore only the onchain wallet. Once the grace of holding the funds is over you will see your sats in onchain wallet.
Meanwhile you can start a new node instance and I suggest to create a new seed, fresh. Leave that old onchain wallet to settle and later you can move the funds into your new created node.
In this way you start fresh, clean and do not complicate more the process.
Also, in case that not all your peers closed the channels, but you still have access to your node data files, you can go into the lnd folder and will find a latest automated backup file of your channels.
See the guide about how to restore your funds from node channels using Blixt here and also in there is specified where is located the automated backup.
Umbrel devs have also a copy of that file, in case you erased that drive or is not accessible anymore. The automated process is that every time you open or close a channel, Umbrel is doing a SCB file in that location and then is uploading that file to Umbrel servers, as an encrypted backup.