Or the corresponding button in the GUI?
That's actually a different mechanism from
sendall, although it should have the same effect.
1. I have imported one of the descriptors (pkh) on the online machine. The daemon has started a rescan. This probably takes a very long time in my case. The RPC call ended with a timeout at some point. But the daemon continued rescanning. Then I terminated the daemon during the rescan as a test and started it again. But it does not continue with the rescan after restart. I know that the displayed balance is correct, but why doesn't it continue the rescan or start it again? I have also reloaded the wallet.
Rescan state is not persisted in all instances. You can trigger another rescan using
rescanblockchain.
2. I have received 4 descriptors with the same pubkey for each legacy address. The types are pk, pkh, sh(wpkh), wpkh. I have now used the pkh descriptor. But could I also use the others? What should I use? I would like to transfer the balance of the legacy address to a segwit address (bc1).
Legacy wallets could receive to each of these address types for any key in the wallet, so the migration creates these (or a combo() descriptor). To be safe, you can import them all, but if you know which address type you had used, then you can just import that specific one.