I found a key which begins with a 1 on my old computer (2013) in a text document and I have been unable to work out the process from
Also know that keys do not begin with 1, Bitcoin addresses begins with 1, 3 or bc1
Address that start from 1 are legacy addresses
Address that start from 3 are nested segwit addresses (also multisig addresses starts from 3)
Address that start from bc1 are native segwit addresses
If this is what you saw, they are addresses, you can also import it on electrum wallet but just to track the address transaction history and nothing more, you will need its private key to spend. If the address is valid also, you should be able to import it.