Bought it right away for my steamdeck. It work well right out of the box. Standard is the default settings and RECOMMENDED for now. It run stable at 30fps for me. I tried 60 fps but it not stable and fluctuate between 40-55 fps. If you want to play higher than 30FPS, change the Max FPS in game to 60. After that set frame limit to 40 in the Steam Quick Access Menu ( depend if you want or not). Moreover, the only time i see performance drop is while being at the area of Village/Town. The scenes happening there also may cause a bit of performance drop. The minimum i ever get is 27 FPS. There is no significant drop while in-battle,other area outside village,multiplayer. Those work without an issue and pretty stable for me.

Edit 1: After few configurations, i find out Proton Experimental give a little bit of boost to fps but not necessarily needed. You may stick to default if it work fine for you. I also use cryoutilities recommended settings and set UMA Buffer to 4 in Steamdeck BIOS. It does make the performance bit better than default. Do this at your own risk and if you know what you doing. If no, just stick to default setting as long it work fine on 30 FPS. Changing in-game setting from Standard to Higher will impact the performance, so just stick to Standard. Additional notes, doing these not even make the area around Village/Town stable at 30FPS. It still can go below 30FPS. The area is not properly optimised. Also, turn vsync off in game settings.

Combat:
The combat is surprisingly smooth and really make me giggle. Pretty impressive gameplay and the AI is smart by default on using skills especially support skill (heal). Not only that, you can customize the skill for the character as you level up the mastery. Having the need to do combo and stop to dodge/guard is also very fun as the boss is pretty challenging.

Steam Deck Control Layout:
The default control on Steam Deck already good enough, but may adjust it to suit your need. As example, i set L4 for sprint as clicking the Left Stick to sprint everytime is quite annoying for me. However, there is in-game setting for auto sprint if you want.

Multiplayer :
It works well for me and there does not seem like there is a much drop when I play. It can run pretty stable without lagging. Take note, you can repeat the quest with the party if you want.

Overall, i think this is a pretty good game to pickup for Steam Deck as not only it can run by default. You dont need much tinkering to play it and just stick to default. The story is quite enjoyable for me, but the cream of the cake in this game is the gameplay. Doing the Full Burst and Link attack is pretty satisfying. However, there is still room for improvement especially around the area of village/town. If you looking to grab a game where the gameplay is very fun and good story, you can add this to your library. I may change my review depending on what i may encounter in the future of gameplay.