Is it, or is not, possible to run arbitrary APK-formatted applications without regard for code signing or any app store[1]? If so, sideloading is not a thing, t

Is it, or is not, possible to run arbitrary APK-formatted applications without regard for code signing or any app store[1]? If so, sideloading is not a thing, that's just the normal way to use a application[0]. If not, the operating system is malicious, and kaszanka's complaint about that fact stands. 0: Provided it runs on your OS in the first place, obviously; adding support for APKs in general is a meaningful feature, in the same way as wine adding support for EXEs on linux. 1: In the same windows has been able run arbitrary EXEs since... well the entire time it's existed, give or take incremental extensions and revisions of the file format.