oh shit! I'm going to try getting this to run on my Deck later for sure!
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EDIT: for people wanting to play it on the Deck like me, a step by step tutorial:
-Turn on Steam Deck
-After it is fully booted, hold the power button, then select [Switch to Desktop]
-In Dektop mode open a browser, go to the link OP posted, and download the game to a folder you can easily find (Desktop or Home for example)
-Unzip the game by hovering over it with your cursor and pressing L2, then select [Extract], then [Extract Archive Here]
-still in dektop mode, open Steam (a shortcut should be on the dektop)
-On the top of the Steam window select [Games] then [add Non-Steam game to my Library], then in the new window that opens click [Browse], then look for the game's .exe you unzipped and select it
-The game is now in your Library, so go back to the Dektop and double click the [Return to Gaming Mode] shortcut which should be there by default
-After your Deck rebooted into Gaming Mode, press the Steam button and go to your Library, and with R1 Switch over to Non-Steam games, where Mega Man X8 should now be in
-while highlighting it, press the Menu button (the 3 Lines button aka. Start) and select [Properties]
-Here you can change the name of the game to be less confusing.
-After changing the name, click on [Compatibility], and tick the box next to [Force the use of a specific Steam Play compatibility tool], and in the dropdown menu that will appear select Proton Experimental
DONE
now you can back out and start the game
for a 90fps lock on the Deck OLED, go into the game's settings menu and select 120fps and vsync off. let the steam deck's framerate limiter handle the rest