Some boxers could, most wouldn't.
Higher weight classes higher likelihood. Without significant cross training someone like Teofimo would lose to anyone with even decent grappling around his size.
But generally skills that translate to being an elite boxer mean they would likely be good at MMA as well (with training).
I recall about 10-15 years ago when I was in socal, sugar shane mosely training at a bjj gym rolling with some decent blue/purples getting tapped but trying to learn. Around the same time Shannon Briggs was teasing a crossover and going several minutes without being tapped at ATT with brown/black belts (they just couldn't take him down/if they did he would stand up Derrick Lewis style).
Style for style of course boxing < worse boxing, kicking, clinch, and grappling. This should be obvious to everyone.
However certain guys in boxing are very athletic and powerful for their size and would be threat to win quickly and hard to take down. I'm not sure if how good they are in boxing is a great measure of it though.
Someone like Tyson Fury who lacks one punch power, and is not physically powerful relative to his size could lose to anyone in MMA, while someone like Dillian Whyte (who Fury easily beat in boxing) can bench 400+ and squat in the 600s and is a much harder puncher would be way more likely to be a huge problem in MMA even without cross training (he has some).
At some point size, strength, natural athletic ability, natural fighting mentality > skill.
I think a HS wrestler could beat Floyd Mayweather. But there are certain boxers who could likely transition and make a run for the title. It's all size and match up dependant.