I have the answer
BSV's lack of replay protection was once again the solution to my problem
This is how I recovered BSV that was sent to pubkey (many years ago):

• First, move BCH and eCash to a new address
• Install a fresh spare laptop (with VPN of course)
• Download the full BCH client (the one Forked from Bitcoin Core) (note: I do not trust this software, but used CoinMarketCap.com to find the "official" website)
• Import the pubkey, let it synchronize the first few years (until the coins show up, but before they are sent out (after all, you just move BCH out of this address))
• Take it offline
• Import the private key
• Create a raw transaction to a new address (this transaction won't be valid on the BCH chain, but will work on the BSV chain). Just in case, I used a legacy address
• Copy the transaction to a USB stick
• Check it (I used BCH's Electrum Fork for this, in a VM), and broadcast it online on the BSV network
• Use another device to broadcast the transaction on the BSV network. I used https://whatsonchain.com/broadcast (on Tor)
• Wipe the laptop (don't let it go online again after you entered the private key!)