It depends on lighting and recoil and numerous other factors. Shooting freshly painted white steel with the sun behind you is easy enough on 4X at 500. Move the sun and change colors and stick the animal in some same-colored brush, and I like having the option to go higher.
My longest shot on a game animal was 451. I used something like 14x. Dialed elevation, no wind, started with scope on 18x and went back to ~14x for a brighter image with more FOV. Didn’t see the hit (recoil) but did see which way the animal ran. He didn’t go far.
I shot last night right at dark at 550 a few shots. 8x was the minimum that allowed me to square the reticle on the target. 14x made it much easier to hold into the wind (about 1.5moa of wind and my first shot was a marginal hit as I underestimated). Even on 14x shooting weak side, I could easily spot hits (or, could see the plate swing on impact - couldn’t see the actual poi because it was near dark).
Everything is a compromise and I don’t think there’s a single answer set in stone. Also, guys with poor vision will be more sensitive to magnification and will likely need more minimum magnification but might be less able to handle too much magnification if lighting is poor.
You really do have to figure these things out for yourself. There’s no single universal answer here. I’ll just say that I personally see 18x, maybe 20x, as an absolute ceiling on any hunting rifle (hunting defined by how I hunt which might differ from you), but others may prefer 12x or 25x and as long as they use it in practice enough to know how it works for them I’m fine with it.
A few years ago I was elk hunting with a guide whose brother was guiding on another nearby ranch and that guy’s client missed a chance at a really nice bull at ~100 yards because he had a fixed 20x scope on his long range rifle. Oops. Don’t be that guy.