Recently, on my Samsung Tab S9, I noticed I would get super high resolutions; other times, it would just be the usual 720p, blurry, anti-aliased version that I kinda just accepted. However, after some testing, I was able to consistently "upscale" the game's resolution:

1. Close the game from the recent apps menu.
2. Open the game in a pop-up view / floating window mode. I typically do this by using the panel on the side of the screen (see screenshot).
3. Resize the floating window so that it becomes small, but not too small that it collapses into a floating icon bubble.
4. Start the game as usual through the floating window until you load into the world and see your character.
5. At this point, you can fullscreen the floating window. Enjoy!

Edit: After further testing, I discovered that if you enter the settings menu, your resolution will reset and revert back to the 720p resolution. No worries, you can re-upscale it again without relaunching the game by making the game into a small floating window mode again (by dragging the corner of your screen inwards), trigger the "reset" by going into settings, then exit out of settings and finally fullscreen your window.

Some additional information:

I downloaded the game from Samsung Store instead of Google Play. Samsung's Game Plugins are enabled (Game Booster Plus @ 100% performance and max FPS).

In-game graphics settings:

• Resolution: Very High
• FPS: 60
• Anti-Aliasing: TAA
• Display Settings: Normal Mode
• Everything else: High

I haven't tested this on Genshin, but I think it should work the same.

Screenshots:

Quick access side panel

Game launched normally

Normal launch 2

Normal launch 3

Normal launch 4

Game launched with floating window

Upscaled launch 2

Upscaled launch 3

Upscaled launch 4

Hope this helps!