It's hard to give a generic suggestion, because it's related to whatever you're plateauing on.
Obvious one is anything related to your job. If you do front end, then animations, architecture, etc. If it's back end, then algorithms, etc. There's plenty on sales, marketing, copywriting, and so on.
Or if you don't have a good job, then a bootcamp and such. Certs are more of a starting point for people with no experience but need to prove their competence. The AWS certs are all very safe bets.
A lot of people like to do free stuff on YouTube or articles only, but the downside is that most of these are half-assed. I've taught classes for years and writing good material requires a lot of effort. It takes about 3 hours of prep and iteration to teach a technical class for 1 hour - stuff can be further simplified, code can be improved and shared, new things updated, and so on.
A level above that is hiring a mentor. Which mentor again depends on what your plateau is on. Most aren't hired directly; you pay in labor and such. Universities are an institutional form of this, but there's plenty other options once you get there.
The most generic suggestion is MasterClass. Watch it past specific things like tennis and chess, and you'll see the principles. Kasparov doesn't open with openers, he begins with the principle that you should attack two pieces at once. A lot of people there have been doing things naturally that they don't even realize what they're doing wrong. One interesting example is David Mamet is one of the best dialogue writer of all time, but he can't explain what makes it good. But there's one by Aaron Sorkin who analyzes his idol Mamet, and he goes into it in a way that us regular people can understand.