The anecdotal MI7 isn't actually that well liked stuff seems silly to me... That's like me saying of 10+ I know that saw Barbie, only a couple liked it and those 2 didn't love it. Everyone else was in the it was fine or it was meh. But, of course, that doesn't mean overall word of mouth isn't stellar.
Let's not pretend people were always too high with where it could get based on TGM. And, let's not pretend it wouldn't have done considerably better had it hypothetically swapped release dates with Flash or Indy.
Sound of Freedom came out of nowhere and absolutely hurt it as similar but obviously not as robust as TGM, MI movies do well in flyover states and red states and that's especially where SoF over indexed.
Barbie and Oppenheimer even hit the late late legs of Elemental briefly. They sucked out the oxygen from everything else. They are the box office right now. I expect it to impact Meg and Mutant Mayhem even a little.
Part One was stupid too. Better to cheat like Fast X and Across the Spider Verse and just not include part one in title. Heck, Infinity War too. General audiences don't pay huge attention to behind the scenes stuff so while us here all knew long, long, long ago that Fast X and Spidey were part ones most others didn't. I mean, after knowing Fallout is essentially Rogue One Part Two as it uses the same exact primary villain and then ties up that storyline so it's always been odd to me that they decided to title it as much. When they hadn't done it earlier. It DID NOT impact the box office as much as SoF and Barbie and Oppenheimer but it was a stupid decision nonetheless.
Those are the three biggest factors with its underperformance along with maybe some slight fatigue.
By all metrics, audience scores are more than fine for it...
Rottentomatoes Verified Audience 94% 4.6/5.0
Letterboxd 3.9/5.0 with 240K~ ratings
Cinemascore A
IMDB 8.0/10.0 with 100K~ ratings (I don't put as much faith in this one as I once did but MI7 film is the type that might get an uncontroversial rating there not voted up or down by many like other stuff there)
...those are all very strong audience scores. Just for a number of reasons, including a few I failed to list, it didn't take off with the same type of legs as Rogue or Fallout.