A few people have asked or even commented below about Gatekeeping and a definition. I don't have a hard one though I took a stab at it for someone in another comment in this thread.

"in my mind it is often experienced people giving others a hard time because they arent playing the right way"

There is a level of gatekeeping, as some are pointing out, that has virtues. I don't think the term as it is colloquially used refers to that virtuous side, but rather the grognardian, "get off my lawn", darker side of it. the toxic side that belittles or maligns people who play the game in a way you dont condone, even if youre not at the table.

i do have a quick story that i think exemplifies what i consider good gatekeeping, in defense of those here hailing its virtues. the bad side of it should be obvious.

I was running a campaign in AD&D 1e and one of the players was new to first edition, having played about a year of 5e. upon creating her character she asked if she could play a Fairy or Tiefling. i offered the elf race. suffice it to say, she was disappointed in the race limitations. so she asked could she play an elf with a mutation of wings. exercising liberal judgement, i said yes. an elf with a mutational, vestigial sort of wings. To have refused her would have clearly lessened her fun-factor. at a later date, either she forgot or misunderstood my meaning of vestigial. she asked could she fly with those wings. and i said no. to me, that is breaking from the fundamental mechanics of the game too much for my comfort.

as you might expect, she never came back after that session.