There are no plans currently to offer Marvel’s-Spider-Man: Remastered as a standalone. In addition, players who purchase Marvel’s Spider-Man: Miles Morales on PlayStation 4 can upgrade at no additional cost to the PS5 version of Marvel’s Spider-Man: Miles Morales and can take advantage of a paid-upgrade to download Marvel’s Spider-Man: Remastered. It also includes three new Spider-Man suits, new photo mode features, new Trophies, and all three episodes of The City That Never Sleeps DLC.Marvel’s Spider-Man: Remastered is an enhanced version of Marvel’s Spider-Man, and is included as part of Marvel’s Spider-Man: Miles Morales Ultimate Edition for the PlayStation 5. Insomniac has previously called its remaster (which, incidentally, won't work with PS4 saves) "no simple up-res", confirming it will feature "better-looking characters with improved skin, eyes, hair, and facial animation ray-traced reflections and ambient shadows, improved lighting, more pedestrians and vehicles stretching further into the distance, and the same optional performance mode offered on Marvel's Spider-Man: Miles Morales".
Of course, those that already own the PS4 version of Spider-Man will be able to play it on PS5, but they won't benefit from the various additions being implemented for Remastered. Notably, Sony says "there are no plans currently to offer Marvel's-Spider-Man: Remastered as a standalone." This option, incidentally, is also available to anyone that buys Miles Morales' standard edition on PS5.
To acquire Spider-Man: Remastered from there, players will need to purchase a paid upgrade, which will cost an additional $20 USD. The first thing to note is that those who buy the PS4 version of Miles Morales (which has no Ultimate Edition option) do get the PS5 version at no extra cost, but only the equivalent of PS5's standard version.