I would tend to ignore the UEFA rules when considering our squad. If we end up in a position where we have a player or two in the PL squad but not in the Europa squad then I don't think anyone will lose too much sleep.
If I consider our squad from a PL perspective then we still have loads of space for more players and can buy association trained players or overseas players whoever we think is the better fit for the position.
OS players at present = 16 (only 13 likely to be part of squad): Vicario, Udogie, VdV, Romero, Dragusin, Porro, Sarr, Bentancur, Bissouma, Werner, Son, Kulusevski, Richarlison, Lo Celso, Regulion, Solomon
Association trained players at present = 7: Forster, Austin, Spence, Davies, Maddison, Johnson, Solanke
Under 21 players at present = 9: Gray, Bergvall, Odobert, Moore, Phillips, Hall, Abbot, Lankshear, Devine
We can sign 2 more players (1 from overseas) even if all of Lo Celso, Solomon and Regulion stick around (which they won't!)
The fact that it is likely we move on at least 2 of those three players (and probably all three) shows that we're absolutely fine in terms of room in the squad for whoever we want to buy.
Our under 21s are also all well under 21 so not even a problem next season.