RetroAchievements for Terraria require tModLoader, which you normally can't run on Android. I tried getting it to work with GameNative, but had no success.
But recently, I discovered this Android app that lets you run desktop .NET apps:
https://github.com/FireworkSky/RotatingartLauncher
The installation is pretty straightforward: you just specify the path to the GOG Linux version of Terraria and the path to a ZIP file containing tModLoader.
For mods, I downloaded them on my PC through Steam and simply copied the .tmod files to:
<Internal storage>/RALauncher/Terraria/tModLoader/Mods
For save files, I set up Syncthing to sync ~/.local/share/Terraria/tModLoader/ to: <Internal storage>/RALauncher/Terraria/tModLoader
By default, the game opens stretched at a much lower resolution, but going to Settings -> Video -> Fullscreen automatically sets the correct resolution.
To log in to RetroAchievements, I had to connect a keyboard to enter my username and password. While doing so, I noticed a small bug: connecting a keyboard while the game is running crashes it.
I haven't seen this app mentioned on Lemmy, so I hope someone finds this useful.
P.S. The handheld in the picture is an AYN Thor.
Do you mean, is there a bigger-screen version of this handheld? No, but it's about the size of a 3DS.
There are plenty of larger single-screen handhelds, though.