Let's change the way we look at this.
Assuming the story is true, Everton want to buy him now because they think a) the limit of his ability is significant higher than his current ability, b) they back themselves to turn that potential into reality and, importantly, c) they are expecting his value to go up and are keen to take a 5m risk now rather than a 10m risk in the future.
We are financially healthy, but cash poor. Selling player will only make a difference if the fee is paid in full up front. Demanding that Everton do that, for a relatively small fee, weakens our negotiating position and will likely mean a smaller sell-on % or maybe no sell-on at all.
Up front payment tends to be a hard-ball tactic used by clubs who don't want to sell, or the buyer is desperate, and where a sell on profit is unlikely. Cristiano Ronaldo to Real Madrid, Maguire to Man United, Ramsdale to Arsenal.
So let's see that 5m, or even 10m, does not really motivate us to sell. We would only accept if we decide that his price is higher than his value, or at least what his value might become as a Sheffield United player. It's also true that a 5m or 10m sale isn't going to strengthen us in the transfer market very much. If we needed that sort of money to finance a deal, they are many ways it can be found and accounted for. An extra debtor just makes buying players less risky as the future income is a bit higher.
However this ignores two relevant factors.
1) the player and his agent. Rejecting an offer from a club higher up the pyramid usually leads to one of two consequences - they'll either be unhappy about it and force a move anyway or they'll demand an improved contract. If the demands aren't realistic it might be in our interests to sell. Pre-empting those moves isn't easy but getting it wrong could cost you the player and most of the original transfer fee.
2) the club who has promoted its intention to be 'self-sufficent' and promote youth. Part of this cycle involves selling players. This doesn't mean selling at the first opportunity but nor does it mean hanging onto players after their sweet spot has passed. Both options are risky.
My view is that, while recalling him has been counterproductive, being around the first team group pushing for promotion will benefit him mentally and the lack of gametime won't be as big a setback as some think it will. I would turn on down anything under 10m, let him enjoy a full season out on loan in 22/23 and then make him a first team squad in 23/24. It's not unrealistic that he could develop enough in the next two years to score 10+ goals in the Championship before he turns 21, and then we'll be talking about more serious player and possible transfer fees that would be harder to ignore.
This isn't a DCL situation, we weren't in a position to turn that down and the funds were needed to support Wilder's overhaul.
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