These are some of my essential Android apps. It's a lot, but I couldn't decide which ones are less essential, sorry. All of them are FOSS and can be found on F-Droid or IzzyOnDroid (F-Droid compatible) repos

• Neo Store is my favorite F-Droid client (F-Droid is essential, but the official app sucks IMO)
• Aegis is a great 2FA authentication app
• AirGuard if you think you might be a victim of AirTag stalking
• AShell (requires Shizuku) for ADB access without computer (you need to be on wifi tho)
• CloudStream when you are too broke to afford 10 subscription-based streaming services
• echo unmaintained but I was unable to find any alternative. It records in the background and keeps the last N minutes in memory. You can save last X minutes as mp3 whenever you want.
• feeder is a great RSS reader
• Inner Tune best YT Music client on F-Droid IMO (I tested all of them I could find few weeks ago)
• KDE Connect - connects you Android phone with your PC
• KryptEY might be useful if EU bans encryption
• libretorrent best torrent app on Android I have used
• Translate You translator app supporting many sources
• unexpected keyboard is my favorite for writing terminal commands in Termux or programming
• Voice is the must have for localy downloaded audiobooks
• YTDLnis is very cool yt-dlp GUI full of features + can be set as downloader app in ReVanced settings
• and the best of all: Termux - Linux terminal on your Android
• bonus: zotify (website) is the only Spotify downloader I know about that actually downloads from Spotify (!). It's a command line app. It can be pretty easily installed in Termux though and usage is not very difficult if you are familiar with the command line. Please read the README. I personally love it.