It doesn't help that even if app sideloading was made possible on iOS, the significant drop in installations will still happen once the apps are pulled from official stores. Most people are not familiar with installing apps from outside of their phone's sponsored ecosystem.
1. How do you access said apps? There has to be some repository storing the apps.
2. Certain regions can straight up ban sideloading by only allowing pre-approved app stores (eg. Mainland China). Ofc there will be technical ways to bypass this, but you are limited by technical knowhow and internal intelligence agencies abilities to find those people.
3. You could make using certain apps with such capabilities illegal. People may try to use it, but if found among a small set of protesters, they can just be "isolated". How do you prevent that?
Sent to you via bluetooth file sharing (an OS feature) by someone else who already has it. Or tor, vpn, etc.
What if Bluetooth File Sharing is disabled via a region lock? (Eg. China)
What if the only VPNs allowed are those that have prior approval from an Interior Ministry?
What if a country initiates Internet Whitelisting at the ISP level for "national security reasons" and requires every user to maintain access logs?
In addition, certain countries may require you to run approved Roms, and if you don't you can face prosecution.
This has been done in action in India with ISPs like Jio to block TPB for example.
Remember - any traffic over the internet can be logged by your service provider (eg. ISP, VPN, etc)
Mass File Sharing Blacklisting has been enforced by Indian ISPs since 2019
VPN+ISP traffic log sharing has been enforced in Kazakhstan (along with SSL stripping)
Blocking Tor downloads has been implemented already (with varying levels of success) plus attacks to deanonomize Tor have started occurring since 2021.
Turkïye has implemented ISP Whitelisting ostensibly for Children but the same core technology can be extended to everything - https://internet.btk.gov.tr/guvenli-internet-hizmeti
App Store restrictions and region locks have existed in Mainland China since the early 2010s.
It's very easy to tamp down and censor internet based communications. Individual corporations have the capabilities to apply such censorship if they wanted to, let alone ISPs.
I'm not raising the bar btw, I'm just someone who works in the intersection of cybersecurity, government, and business.