I've heard that before - yet it has newer made sense.
A single, centralised App repository (or "Store") run by a single gatekeeper as a software distribution model is the best any controlling government could want!
Encrypted communication? There’s no easier way to discourage or abolish encrypted communication if you all you have to do is regulate a monopoly or duopoly of mobile application stores: Make any app distributed subject to obtaining a government licence. Easy-peasy, if you only need to force the hands of one or two operation systems and/or App Store operators in a duopoly (by, for example threatening a ban on device sales) Make them pull any non-complying messenger app from their stores.
Don't like VPN tunnels? Just ban them outright. The idea is certainly not new
to the Chinese.
Want to control the political narrative on social media? As MacBH928
correctly said above, the version of Telegram available from Apple's App Store has censored some channels.
Whereas sideloading enables users to install
unregulated apps that use end-to-end encryption that has not been weakened by government intervention - and can access Telegram groups uncensored.
👉 If I were a big, controlling, possibly evil government wanting to ban end-to-end encryption... the first thing I‘d do is outlaw sideloading.