What is the proper way?

[junior_clk]

Hi
I got a start9 full server with electrum
A offline laptop with sparrow and a online with sparrow connection to the start9 node
And a Tresor Safe 5

I used to mine in 2011, so it is a legacy address starting with a 3  P2SH as discribed in BIP13/16? its single key
I got the 64 character private key and/or WIF
never made a transaction so I don't know the UTXO

On what laptop should I do what to make a PSBT and sweep everything to the hardware wallet?
I understand that the offline laptop is for signing

[nc50lc]

I used to mine in 2011, so it is a legacy address starting with a 3  P2SH as discribed in BIP13/16? its single key
I got the 64 character private key and/or WIF
never made a transaction so I don't know the UTXO

If that WIF starts with "5", "K" or "L", then it's WIF.
If you mean it's just the 64characters, the private key is hexadecimal and needs to be encoded to WIF before it can be imported to your offline machine.

For the latter, one option is to download Bitaddress source code (GitHub Link) then transfer and extract that to your offline machine,
You can start its html file using any non-dated browser.
From there, you can go to "Wallet Details" tab where you can encode your private key to WIF. (finish the 'Generating Bitcoin Address' procedure first)
You may import both compressed and uncompressed WIF to your offline wallet.

BTW, last time I checked, Sparrow doesn't support single-key import so your next best option is Electrum since you're using an Electrum server.
For that, you can follow these instructions (with screenshots): /index.php?topic=5524213.msg64885706#msg64885706
Notes: use your WIF in place of the mentioned "mini-private key"
And in the online machine, you may create a dummy wallet to be able to set your server in the network settings (green/red circle icon) before you create the imported watch-only wallet. Or launch it with -1 -s <server:port> to immediately set your own server on start.