Hey I am fairly certain you can't disable them but you can choose not to follow them or listen to other playlists/albums with that artist. As far as I know they will always show up, they will however show up less frequently in your "discovery" tab if you do not follow any "this is playlists" and don't listen to them.
At least that is what I am guessing. I am going to copy paste my response to another thread on the matter just in case any information might be helpful:
I think that the "This is:" (with the colon) are curated by a human editor (as opposed to updated algorithmically) I have a "This is" (no colon) playlist and have noticed that it ("This is Kid Indigo by Spotify") updates regularly (presumably based on recent stats) as opposed to a "This is: Animal Collective" playlist that I "liked", which I noticed not only has a custom made album cover but also has a past date for most of the songs on the list.
I believe it is kind of more set in stone so to speak, perhaps for more popular artists who are also prolific, to keep some consistency to their "essentials" playlist rather than updating with each new release (that may gain a lot of initial traction but is perhaps not truly "essential", ya dig?)
Anyway, all of this is just gathered assumptions on my end but maybe it will be helpful. For reference I will link the "This is Kid Indigo" playlist. I think it is a particularly interesting example for anyone curious about this feature as my overall follower/play count/ etc are all quite low but perhaps there are more complicated algorithms at play that take into consideration other aspects of an artist and their listener base.
https://open.spotify.com/playlist/37i9dQZF1DZ06evO1YHHkn?si=8GfderS6QP2X9ClcBGe9XQ