I don't use cleaner apps for several reasons, and there's nothing they can do that I can't manually do myself. I doubt it'll help you in this case anyway. I'm one of the biggest fans of the V20 you'll find, but it's getting up there in age and lag is gong to be an issue. It's running 2016 hardware, but most apps have been updated multiple times since then. With most updates comes extra functionality and extra need for resources. Even the coding of websites like Facebook (a known resource hog in its own right) change over time.
It's just the nature of the beast when you can't upgrade a phone unless you replace it all together.