I used to but not anymore. Sometimes IMDb has niche movies which are devoid of reviews, but then writing one means I work for free for a private company with no ethics making tons of money so the eff with that.
I only use imdb to look up cast names, I don’t look at reviews (let alone write them). I’ve never used rottentomatoes or metacritic either.
I (sometimes) used to leave reviews on reddit, always in new episode posts on a tv show’s sub.
Nowadays, I might plausibly leave a review in the comments on a relevant post here on lemmy, or if my opinion was solicited in one of the discord servers I regularly spend time in.
i mainly just use letterboxd, and the way i use it is more like a casual journal rather than something that would be useful for other people to read (and i state on my profile there that i'm not trying to give objective critique at all)
the other place i talk about what i watch would be in chat servers and even then i don't like to get into the weeds with discussion too much, if someone asks i will give them my opinion and maybe if i am interested we might talk about why we disagree on certain things but it isn't something i want to spend a lot of energy on