Not sure if other folks prefer this, but I really enjoyed Deus Ex Revision, which is up on steam and I works fairly well on steam deck with some tweaking:

https://store.steampowered.com/app/397550/Deus_Ex_Revision/

I haven’t played the game myself but this thread on GOG might be a good place to start: https://www.gog.com/forum/deus_ex_series/mods_for_deus_ex_graphics_gameplay_and_more/page1

Great post, I have wanted to play it too! But I felt the age might hold it back

https://gmdxmod.com/ is the best way to experience the original Deus Ex imo.