Since it's monthly, probably at least 5. It was incredibly hyped, and people want to see what is actually going on. Hickman's X-Men books, fresh off of HOXPOX, went as follows (on ComicChron, so this is sales to store, which we know is a bit different):
X-Men 1: 255K
X-Men 2: 117K
X-Men 3: 103K
X-Men 4: 93K
X-Men 5: 80K (shipped twice that month)
X-Men 6: 92K
X-Men 7: 76K (shipped twice)
X-Men 8: 75K
X-Men 9: 70K (shipped twice)
COVID
Huge, unsustainably large first issue sales, still very high through issue 3, then it started slowly finding its level by the fifth or sixth month. I'm sure the same general pattern exists for USM, although the levels might be vastly different. At a guess, I'd say ASM is selling somewhere around 50-70K right now, which would imply USM 3 is between 110-155K. Very, very good, and will still be selling quite well even if it has another ~30% attrition in the next two months.