Fake-08 development trails PICO-8 so it's possible your Fake-08 version is out of date, the cart is made with a newer PICO-8 version, or the cart is just plain incompatible with Fake-08 (many carts do not work with Fake-08).
I have a couple handhelds like yours and the official raspberry pi PICO-8 build works great on them - I suggest you get a PICO-8 license and check your distribution's documentation to learn where to place the raspberry pi PICO-8 binary in the filesystem.
I didn't do any fancy mounting, as far as I can remember. I think it really was just a matter of copying the directories to my SD card and replacing the directories on the deck with links to the ones I copied to the card.
I'll take a look at what I did the next time I get the deck out and let you know
Really grinds my gears manufacturers pretend the beveled screens are premium features and not the ugly, difficult-to-protect liabilities that they actually are.
Not directly relevant but if you have the 64gb deck and a big SD card: you can symlink the directory that houses all the proton versions and shader catches to the SD card.
That was pretty much the first thing I did after I got my deck, as a stopgap before I could upgrade the SSD but it's been working well enough I never got around to swapping out the SSD after, what, almost two years?
Any progress/news re: C# web export?