From what I've heard from friends who live there permanently, all of these apps are legally banned because they don't have a license to operate. The government filters them so that regular users can't use most of popular texting apps, forcing them to install a VPN on all their devices for a monthly subscription. However, it's easy to see that this ban doesn't help at all because everyone uses a VPN.
In Qatar, for example, WhatsApp is essential for all businesses and provides a great service. However, it can only be used via a VPN, and those who can't use it resort to the IMO messaging app. There may be other reasons we're not aware of, but I don't think they're valid.
The funny thing is that messages via WhatsApp and Telegram can be sent without a VPN, but calls don't work anymore. If the ban is formal and no one is fighting it, then there is no ban.
I have not seen or heard of anyone checking people's phones for illegal apps in these countries.
If you fly to Russia, your phone and correspondence can be checked, and there are people at customs who know English, Arabic and other languages.