what kind of apps cant be updated through playstore/fdroid?

it's not that they can't be (maybe some apps I use can't) but rather that I don't like some things about F-Droid. One of the big things being unreliable app updates. They are often significantly outdated compared to GitHub releases.

https://www.privacyguides.org/en/android/#f-droid

"Due to their process of building apps, apps in the official F-Droid repository often fall behind on updates. F-Droid maintainers also reuse package IDs while signing apps with their own keys, which is not ideal as it gives the F-Droid team ultimate trust."