Ah, Linux, you gotta love it right? There's numerous different ways to do the same thing. One of those that people like to argue about is packaging and how to install things on Linux. Flathub with Flatpaks at least seem to be popular and it keeps growing.
Cassidy James Blaede just wrote up an official blog post going over some numbers, and it's quite impressive to see. To date it shows that Flathub has served just about 1.6 billion downloads, has over 2,400 apps (850 of which are Verified by the author) and there's now over 1 million active users too. Their public dashboard has some pretty fun stats.
One of the big reasons for the growth no doubt is the Steam Deck, which has a full KDE Plasma desktop mode in SteamOS, and has Flathub for all the extra apps and games you can install. A point that was touched on in the blog post noting that some of the most popular downloads on Flathub are emulators and game launchers.
It's not just Steam Deck though with Flathub being included out of the box across the likes of Clear Linux, Endless OS, KDE Neon, Linux Mint, Pop!_OS, and Zorin OS and Fedora 38.
I think Flathub is great personally, it's often made it far easier to tell people where to grab something that's actually up to date. Telling people "it's on Flathub, install via GNOME Software or KDE Discover" makes Linux a lot easier.