However, if you want to install any software on Android, your options are either to get it from the Play store, or turn on sideloading capabilities and download it from another source. This latter option is considered risky, to the point where the argument has been posed to remove the ability.
Seems to me the insistence on locking out the very people who *bought and paid for* their devices is wrongheaded in so many ways. You need a security patch the vendor hasn't provided? Tough luck sucker, cough up money for a new one and toss your old one in the toxic landfill. You want to secure your device further than the vendor's (or even Google's) failed attempts at it (such as parental controls for a child's device)? Too bad, you are forbidden the very root access you would need in order to do a proper low-level configuration.
Heck, even on your most cluttered crapware-infested and insecure MSWin preload, you could at least wipe the system and do a clean, stripped-down install of an OS (excluding those abominations with locked-out "secure boot"). Android forbids that *by design*. Properly done, an Android system would have it's OS on a removable flash-storage that could be pulled, reformatted or replaced (much as you could pull and replace a HDD in a PC now). But we aren't "customers" to the Android vendors; we're just sheep to be fleeced.