Illegal since getting all possible 8 white and 4 black promotions with only 4 captured black pawns requires white to get doubled pawns on each file pair a-b, c-d, e-f, and g-h, inconsistent with the remaining white e and f pawns.
Note that leaving white pawns on for example f and g files would have made this legal.
4BB1q/P1n1KRBq/7b/r1p1PQQ1/4NRR1/rRN2P2/3Nn3/1rkb1b2 b - - 0 1
No Checks wx 0 wp 3 wpr 5 wpx 0 maxuwp 3 minopp 0 bx 4 bp 1 bpr 3 bpx 4 maxubp 1 minopp 0
Illegal since getting all possible 8 white and 4 black promotions with only 4 captured black pawns requires white to get doubled pawns on each file pair a-b, c-d, e-f, and g-h, inconsistent with the remaining white e and f pawns. Note that leaving white pawns on for example f and g files would have made this legal.