You can buy silicon flaps that slip over the top and will keep them comfortably in your ear. The problem is that they don’t fit in the case with the flaps on.
I haven’t tried AirPod Pros but I assume they are better in this regard.
I actually have no problem with the origin AirPods, but the AirPod Pros always slip out of my ear. The former relies on the shape of your ear to hold it in, the latter relies on friction of the insert in your ear canal; and I guess my ears are just unusually slippery. I've tried all the different sizes, and not found anything that works. When I'm working out or cycling I always use the original AirPods.
YMMV of course.
But the worst is that sometimes my own voice resonates back in my ear, its hard to describe but very unpleasant and disturbing in a conversation.
Like you it’s worse in my left ear too.
That earbud style just fundamentally doesn’t work for some anatomical reason in a percentage of the population.
Does anybody else with "wrong" ears used to get awful outside ear pain with the old all plastic iPhone earbuds? I physically cringe in pain just looking at them.