The first step to getting Persona 5 Strikers running on your Steam Deck is to install a custom version of proton. Specifically, you'll be installing one of the most widely used versions of proton, Proton-GE.

You can enter Desktop Mode on your Steam Deck by holding the power button for a few seconds and then selecting the "Switch to Desktop" button in the menu that pops up.
Within Desktop Mode, open the Discover app store and search for "ProtonUp-Qt" and install it.

Within Desktop Mode, you should have installed ProtonUp-Qt by following this guide's previous section. You will now use the app to install the latest version of Proton-GE onto your Steam Deck.

If you are still on the screen you installed ProtonUp-Qt on, you can just click on the search result one more time, then hit the launch button in the top right corner.

Otherwise, you can press on the Steam Deck logo in the bottom left and search for "ProtonUp-Qt" the same way you did in the Discovery app store. Then you can click on the search result to launch the app.
Once running ProtonUp-Qt, click on the "Add version" button. Proton-GE should be listed as the default compatibility tool, but if it isn't you can select it from the top dropdown list. Once Proton-GE is selected, select version 8-27*. Simply, then, hit the "Install" button and let your deck do it's thing. This can take anywhere between a few seconds to a few minutes, so be patient!

* Updated 5/7/2025: Several users in the comments that more recent Proton-GE versions (As far back as version 9-15) cause incompatibility issues such as boot loops and black screens. Use Proton-GE 8-27.
Once Proton-GE is installed, you can return to Gaming Mode on your Steam Deck. You can close ProtonUp-Qt with the button in the top right of the window, and then return to game mode with the "Return to Gaming Mode" button on your desktop.

Now that you are back in Gaming Mode, you have to set Proton-GE to be used when launching Persona 5 Strikers. This is done in a few simple steps.

Find Persona 5 Strikers on your home screen, and press the A button as if you were to launch it and start playing. This will bring you to the Game View screen.
From the Game View screen, navigate to the cog on the right, then to the "Properties..." menu at the bottom. On the left side-bar, go to the "Compatibility" menu, and check the box labelled "Force the use of a specific Steam Play compatibility tool". Interact with the dropdown menu that will appear below, and select the installed version of Proton-GE.

Setting Proton-GE as your compatibility tool of choice will allow Persona 5 Strikers to at least launch, and it will be nearly playable! Stopping here will make the game playable, though it will still have many issues. Cut scenes will not have proper voice acting or audio, for example. This final adjustment to your launch options will fix any remaining issues and make the game fully playable.

After setting Proton-GE as your preferred compatibility tool, you can use the left side-bar to reach the "General" settings tab. From here, scroll all the way to the bottom.
The very bottom of the tab has a text-input section labelled "Advanced users may choose to enter modifications to their launch options". Within this textbox, paste the following launch option:
Copy it exactly as written, and do not add excess content unless you know what you are doing.

Congratulations! You can now play Persona 5 Strikers anywhere you go using your Steam Deck!!

Naturally, I did not fully come up with this guide myself, and the credit to the fix goes to ProtonDB user Swish,[www.protondb.com] who was the first person to mention the custom launch option fix.

Furthermore, I would like to extend great appreciation to GloriousEggroll on Github[github.com], the developer of Proton-GE. Many games would not be running on deck at all without his efforts.