Like A Dragon: Ishin! is a Yakuza spin-off with real time combat, lengthy cut scenes and weirdly capped 30 FPS cut scenes in some cases. Having said that, it deserves it's Verified Status on Steam Deck and you have some options available to you depending on your preferences.

If you can handle 30 FPS then 30 FPS Cap in-game and High preset, no FSR is a great way to play, but if you want a few more frames with little difference in the graphics then our best settings are:

Medium Graphics preset, V-Sync on, FSR 2.1 off and Steam Deck capped at 40Hz refresh rate with the 40 FPS cap.

This will give around 2-3 hours of battery life and give you a solid 40 FPS experience 98% of the time. For some finishing moves, the FPS does drop down slightly but that seems to be mostly the style of screens and the game not the FPS out of sync.