Someone said that, because of their transfer policy, their slider is 100% wages and 0% transfers, which is a great way of thinking about it.
I got you. I'm not sure Broja gets 20M (partially because I think that it would be hard for Arsenal to get that much for Nketiah, who is more proven, although older), but just looking at Hall/Maatsen, they should have ~350M to spend. Add in ZIyech/Broja/Kepa and random other sales (such as, potentially, Humphreys, Anjorin, Hutchinson, Fofana, Burstow, Lukaku, etc.) and Chelsea could have a bunch to spend without factoring in Gallagher.
Of course, you then have to factor in whatever new rules the EPL is coming up with, but looking purely at accounting values, it isn't hard to create a scenario where Chelsea can reasonably spend a bunch of money.
The caveat here is no one actually knows how these players are booked and you have to factor in wages, etc. The real issue for Chelsea is what happens in two or three years if they keep spending and run out of homegrown or fully amortized players to sell.