Over the years of interacting with and observing fandom, I have come to dislike fandom and shipping culture for many reasons. One major reason I want to talk about here is the "Designated Lesbian Syndrome" phenomenon.
I first encountered this term from this Tumblr post made by user desolationlesbian:
Designated Lesbian Syndrome (n.): When fans of a piece of media pick two female characters and pair them together as the token F/F ship and put them in everything, but do not bother to engage with their dynamic in any way more substantive than having them hold hands in the background. Everyone agrees it’s a good ship and it has nothing but their full support, yet this never materializes into real effort or content creation.
Most common with works that have little-to-no narratively important women, but in rare cases can even happen to major and complex characters who are then reduced to token background lesbians as everyone hones in on the boys.
The example I am most familiar with is the fandom of Grand Admiral Thrawn and the Chiss from Star Wars — specifically, some shippers of Thrawn/Eli Vanto, also known as Thranto, pair Ar'alani and Karyn Faro as their token "pair-the-spares" femslash ship. However, while Thranto shippers have create fan content about the Ar'alani/Karyn Faro ship, they do not do it with even a fraction of the interest and enthusiasm as they do Thranto. This is evident in the difference between the amount of fan works these two pairings have received on Archive On Our Own (AO3): as of this writing, the Thrawn | Mitth'raw'nuruodo/Eli Vanto tag contains 1,358 works, while the Ar'alani/Karyn Faro tag contains 34 works only. It is also worth noting that if you use the tag page's filter function, you will notice that out of these 34 Ar'alani/Faro works, 23 of them are also tagged with Thrawn/Eli Vanto, proving the significant overlap between Thranto and Ar'alani/Faro shippers.
Part of the Designated Lesbian Syndrome also involves shippers headcanonning the female characters who could be considered "threats" to their favourite ship that involved male characters as lesbians. It does not matter if the female characters are actually romantically involved with the male characters' in the source material or not. Thrawn never has a canon love interest in both Legends and the Disney continuities, but the fact that Ar'alani and Faro are close to Thrawn as his long-time friend and protégée respectively is enough to make them the go-to candidates for lesbian headcanons from shippers who ship Thrawn with anyone else. Lesbian Ar'alani and Faro headcanons are most common among Thrawn/Eli shippers, but I had seen at least one Thrawn/Governor Pryce (a pairing that I cannot stand at all) shipper literally headcanons Ar'alani as a lesbian so Pryce does not need to worry about Ar'alani fighting with Pryce over Thrawn.
Ar'alani and Karyn Faro are unfortunately perfect examples of the above post by desolationlesbian of major female characters who are reduced to token background lesbians by shippers. As a huge fan of both Ar'alani and Faro as characters, I find it immensely frustrating, to the extent that the Thrawn shipping fandom has utterly turned me off on both Thranto and Ar'alani/Faro ships.
As a lesbian myself, I loathe the Designated Lesbian Syndrome with a passion, because this phenomenon is literally tokenism, specifically tokenisation of lesbians. As a consequence, I have reached the point where when it comes to fandoms with big Male/Male (M/M) ships that are not canon, I only trust lesbian headcanons from fellow lesbians. Yes, this means I do not trust lesbian Ar'alani and Karyn Faro headcanons from people who are not lesbians.
I really hate that it comes to this because as a lesbian, in theory I am in favour of lesbian headcanons for female characters who are cishet-coded or who do not have a canon sexuality. Unfortunately, lesbian headcanons have been used as a progressive way to get female characters out of the way of Male/Male ships (and occasionally Male/Female ships as well, though this phenomenon is more common in fandoms of M/M ships), not because these shippers actually care about lesbians and the female characters.
These shippers rarely put as much energy in talking about or creating fan content for the female characters they headcanon as lesbians as they do the male characters from their ships. These shippers can pretend they care about lesbians all they want, but my lesbian ass can see through their performative bullshit, and recognise their lesbian headcanons are nothing more than tokenism.