Apple has detailed the threats that sideloading of apps poses on user privacy and security. An executive has also stated that iOS is not the platform for you if you want to engage in this activity.
Google has put out a warning to owners of newer Huawei devices against sideloading its apps. Google has been banned by the U.S. government from including its apps on Huawei devices since last year.
A new report goes over, and fills in some of the blanks regarding, the restrictions imposed by Microsoft on Windows 10 S, which go beyond just disallowing traditional x86 apps to sideloading and more.