As you may have seen, @pixelfed has made changes to its software so that it is now compatible with most Mastodon apps.
This means (if the new feature is working correctly!) you can log into your PixelFed account on a Mastodon app, as long as your PixelFed instance has updated to the latest version of the software. Ask your instance admin if you're not sure.
The Mastodon app compatibility is brand new so it may have bugs. The PixelFed team has asked people to let them know if they have any problems.
Alternatively, there's a dedicated PixelFed app for Android called @PixelDroid which is available from @fdroidorg. There's a guide for installing F-Droid at https://switching.software/replace/google-play
Also, there's an official dedicated PixelFed app on the way for Android and iOS, though it hasn't been released yet.