Facebook, apps in BBW that were dependent on Adobe Flash that the Dev gave up on after 10.2.1, Whatapp after June 2017, Android apps that require at least 4.4+ to run, native Bloomberg app for Passport users, banking apps with mobile pay options...
That's what I came up with in the first minute. I'm sure if I wanted to spend the time, that list would be much longer.
RedBerry Passport /10.3.3.2049 / Telus