Uneven buttocks

It is pretty common. My glutes look the same but my left is weaker and doesn't activate as easily. Over time it got better doing more unilateral activation work. Check out these articles which may help:

https://bretcontreras.com/how-to-fix-glute-imbalances/

https://bretcontreras.com/2-1-method-fixing-glute-imbalances/

It is quite common to have a strength imbalance between your two legs.
Researchers have measured the leg strength of soccer players. Now, you would think that nobody would be more even than someone who runs, runs, runs, right? They sprint. They are always on one leg and, over time, that has to even out with all the steps they take. (An average of six miles per game for professionals.) But, no. Those measurements showed that it is not uncommon for players to have as much as a 20-30 percent difference in strength between legs.
It is just the way we are. We have a dominant side.
Can you work on it? Sure. Imbalances aren't good if they are too pronounced. But you might be best off if you blend that work with a bit of acceptance too. It appears it is normal and inevitable too.

your mileage may be different from mine. but if i had my start to do over again, i would have paid more specific attention to my own imbalances. i did ask a physio about it two or three years ago, and he told me it's 'not as big a deal as some people think' and it would equalize on its own if i paid attention to it.

i have been paying attention, but i have some mechanical restrictions and some veerrrrrry old movement patterns from an injury to my left foot in my teens. so he was wrong in my case: it wasn't enough. it's not that i'm not strong on both sides, four years later. and i don't really look any more wonky than anyone else. but my left-right recruitment patterns are so different that inside the skin my left side is often using a completely different set of muscles from my right side, to do the same work. i compensate like a boss, because the whole problem seems like it starts from my feet.

i really don't advise this, is all i'm saying. so i'd keep an eye on it and if you continue to have nagging Stuff going wrong, i'd follow up. for instance: take off your shoes and socks and see if you can do the same stuff with the toes on both feet. if not, work on that because the cliche about every lift starting from the relationship between your feet and the ground is not a cliche after all. it's the truth.