what synchronization you want to use fedora you don’t need to login anyaccount but fedora provide option like google and nextcloud if you login with them it will be synced.
as per i know fedora does not provide a mobile optimized version of fedora but for fedora gnome and kde i think technically it can be installed and gnome shell is optimized for mobile foe a while now kde as well hence it be installed i have not done it but i think
postmarketos is a good option
Mobian OS is debian base os ubuntu touch. porsh is a option as well.
I finally swifted and bought a Linux based smartphone: The /e/-phone from Murena https://murena.com/products/smartphones/ It is a De-Googled and Apple builded on an Android 12 platform which gives modifiers freedom to hack and develop in an Open sourced OSM. I bought the Fairphone 4 which is very suinstable and where it is possible to remove the battery and change camera. The /e/-OSM is now very stable and run very smothly with a Fedora OS and other apps based on Linux kernels. I still miss an ask.fedora.org app which can be found and downloaded in the App loung or at Fdroid or Aurora. But even though Nextcloud and other projects are already in sync.
i dont know why that is bit strange that you want all devices with fedora whatever maybe you like the name or logo.
if you like to have a app in a phone there is a good option just install brave or bromite browser i prefer this not chrome due to privacy issues and then open https://discussion.fedoraproject.org login
then go to top 3dots and tap install it will install a pwa app in your mobile and it is good.
now as far as i know manjaro and postmarket porsh porsh is better i think as it runs all purism libream 5 and mobian for debian
mobian is not by the official debian guys maybe it will be in future arch also support.
and fedora is working on i think you know fedora is heavily sponsored by redhat but still it is a community owned distro so you can expect to have support for mobile.
but if you want to be more involved and the the progress and what to give your opinion join its matrix. i will give a link.