A gatekeeper is someone who seeks to bar certain members from a community. This is often done in an attempt to create security through kicking out perceived outsiders or threats. However, this often excludes legitimate members from a community. Gatekeeper tends to be seen as an insult, as the person excluding thinks they are not leaving out legitimate members.
Transmedicalism is the idea that physical dysphoria is the only and most important qualification for being trans. They have diverse views of who this includes and excludes, but they are known for excluding nonbinary people, stating that there is no nonbinary body for which to strive. They are also known as "truscum" derogatorily.
Not everyone in the LGBTQIA+ community agrees that asexual and aromantic people are inherently LGBTQIA+. They see asexual and aromantic people as invaders, people pretending to be these things to gain access to LGBTQIA+ spaces. The extent of the exclusion can vary from only barring cisgender, hetero asexual/aromantic people to claiming that all asexual and aromantic people are "invaders".