Cleaner apps are not so much a bad idea, it's more that there's a lot of bad cleaner apps. Really bad. And the reality is that they are rarely, in fact almost never, actually needed . I have run most of my devices their whole life and never used a cleaner. A couple of times since starting with Android v1.0. They just don't make a significant difference in a good way. But a bad one can cause havoc.
That said, if for some reason you think you have to have a cleaner (you don't) SD Maid is the best - and safest - one I've seen. Unlike other so-called cleaners, SD Maid only does what it should do - clear out junk files, clean up databases, etc. It does not try to do things it shouldn't. There's no RAM cleaner/optimizer, no cache cleaner automatically deleting useful cache files. It does not run in the background, only when used. No nag ads. Just a powerful set of useful tools for doing useful things.
But...it is a powerful set of tools. And remember, use of tools like this are seldom, usually never, actually needed. Use it very rarely, with extreme care and at your own risk!
https://forums.androidcentral.com/e...ps/details?id=eu.thedarken.sdm&token=N4DSOFk_
Android since v1.0. Linux user since 2001.