Interesting little tit bit,
Whilst Salah has been shopping around (pre Mbappe decision). Mane privately told Liverpool he was leaving a few months ago, Liverpool immediately went looking for replacement & asked Salah to stay & be open to discussion on a new contract.
At present Salah, still on course to leave once contract expired, unless someone offers Liverpool a decent price.
This would explain, Liverpool seemingly quick action on replacing Mane.
United on the other hand, have known for a year who is leaving etc, & only started discussions on transfers recently.