The episodes still get matched to the wrong show, because there's no way to manually fix match on individual episodes. So instead of having episode 1, 2 and 3 of Steins;Gate 0, it now says I have duplicate versions of Steins;Gate episode 1, 2 and 3. The files are named correctly.
There's no need to fix-match individual episodes if you named them correctly (no offense).
That means you've named the files in a way that Plex believes they're the same ones during scanning. This is happening before Plex even looks for metadata.
In your case, files are supposed to be named like this:
TV Shows <- your tv show folder that is added to the TV Show library
.. Steins;Gate 0 (2018)
.. .. Season 01 <- 2-digit season folder
.. .. .. Steins;Gate 0 (2018) - s01e01.ext
.. .. .. Steins;Gate 0 (2018) - s01e02.ext
.. .. .. Steins;Gate 0 (2018) - s01e03.ext
You could include the title of the show as an optional suffix. This is however neither necessary nor will it show up in Plex or be used by Plex in any way -- hence I've just ignored them.