Yes. Developers need to recompile their apps for the 64-bit phones. Some unmaintained apps will naturally have dropped off.
See: Apps that haven't been ported to aarch64 (Store) for efforts on recompiling and/or taking over maintainership. There are some other threads too.
(And do search before posting)
Edit: sorry, this thread with basically the same name is more relvant: Apps that haven't been ported to aarch64