I'm not sure either - the need (if need there is) would be for an out and out LB should we want to go 4 at the back. Solly and BDB are fine as LWBs, but neither of them is really suited for LB. I've got a feeling that might apply to Karbownik as well.
Tbh I don’t really get the clamour for a new LB. Solly was immense prior to his injury, and Dan Burn is brilliant in his own way.
Forward options are far, far more important to improve.