To make way for the upcoming Final Fantasy 1-6 Pixel Remasters, the current versions of Final Fantasy 5 and Final Fantasy 6 will be pulled off Steam later this month. Since these are the ugly mobile ports, I think it's safe to say they won't be missed, though. Both Steam pages for Final Fantasy 5 and 6 have been updated with disclaimers that they'll "no longer be available for purchase after July 27th 2021". They then say you should buy the remastered versions instead which are "coming soon".
Each of these remasters has a rearranged soundtrack, new pixel art, and updated menus, although it looks like people aren't too happy with the reworked fonts. I'm not that picky when it comes to this stuff, but yeah, it's an interesting design choice, to say the least.
Squeenix made a bunch of ugly versions of classic Final Fantasy games for mobile, which then they brought to PC. When Katharine and Brendan ranked the best Final Fantasy games on PC, Brendan called FF6's port "horrible-looking", while Katharine wasn't a fan of its "ickily prettified sprites and nasty fonts". The consensus? Good game, terrible port.
It's worth noting that only FF5 and 6 have been marked for death at the moment, which makes sense. FF1 and 2 aren't on Steam yet anyway, while the current versions of 3 and 4 are the much lovelier Nintendo DS ports, which weren't hounded for being horrid, so Squeenix have clearly deemed them worthy enough to stick around.
You'll be able to buy each of the Final Fantasy Pixel Remasters individually, or splash out and buy (seriously, don't), the entire Final Fantasy 1-6 Pixel Remaster bundle for a whopping £55/$80/€70. Going by each of the Pixel Remaster Steam pages, FF1, 2 and 3 will all launch on July 28th at 5pm BST (that's 9am Pacific). As for FF4, 5 and 6, they'll be arriving at a later, currently unknown date.