First, this app has two versions - SD Maid (which is quoted in the link, recognizing by app logo since I have both versions on my device) and SD Maid SE. I can't link them (see next bullet). The former is in maintenance mode only and mainly targets older versions, while the SE versions target newer Android versions.
Second, both versions are currently banned
from Play store due to Stalkerware policy (IMO blatantly unfair when the developer has to justify in limited text to a bot, without any human interaction)
Third, the SE version is open sourced (unlike the earlier version) . Quoting from Corpse finder section of the Github, depending on the filter you applied (important), it looks for the following places to clear corpse data:
Sdcard
Public media
Public app data
OBB resources
Private app data
Dalvik cache
App libraries
App sources
Private app sources
Encrypted app resources
Somebody who understands code can interpret better from the Github code or check in Discord channel
PS: If you decide to sideload either version of the apps make sure that you disable Google play protect, else it is possible that it may silently uninstall as per policy
It may deactivate or remove harmful apps from your device.
It may reset app permissions to protect your privacy on certain Android versions
This is applicable as long as the ban (second bullet) continues
