i think you're asking a specific question very broadly. you're asking "how are cishet people generally viewed?" but you're really asking "what does LGBTQ places are not to be used by cishet people" mean

that's a pretty unhelpful rule of thumb. generally speaking, there are a few relevant categories of LGBTQ places. in real life, these are clubs and specific meeting groups, which, unless otherwise stated, are generally for use by people who identify as some flavor of queer and cishet people shouldn't take up space. but there are also things like, idk, queer night at a bar, that's probably still fine, just don't be surprised when queer shit's happening

there's also online LGBTQ spaces. ones like this one are fine for cishets to use. i mean, you're posting here now, right? but there are smaller spaces and generally the smaller the space, the less you should participate. but also, the smaller the space, the more niche, so i mean, you're probably better off posting in a space like this, anyways

it's honestly not that difficult to gauge for yourself. if you're not sure, observe the space without participating. look at the tone and assumed contexts of the posts. does it seem like it's queer people talking about queer shit or is it more of a mixed discussion space like this community? if it's a meatspace location, you should be able to easily tell by the body language of the people inside. if they're looking at you like, are you lost? what the fuck are you doing? then you have your answer

it would help to know more details about why you're asking. are you just worrying about an abstract situation because you feel the need to be prepared, or do you have a specific intention to go into a queer space and want to be sure you're not intruding?