I cant deal with the cognitive dissonance
Using they for a neutral and unknown individual causes no problems because you don't have any knowledge of the person or anything in mind when speaking - eg the situation 'Someone has left their bag. I hope we can return it to them' is
easy to say because we have the idea of a person, a individual, an otherwise blank 'human shaped space' and its fairly easy to use sex neutral terms for this.
To swap 'they/them/theirselves in for sex based terms when we have interacted with the individual and have a clear idea in our mind what sex they are and thus would be naturally using the gendered pronouns of our native language takes a
mental work because we have to consciously overcome the dissonance of it - and using neopronouns is also very difficult for this reason. Im sure someone has linked in the thread to the Pronouns are Rohypnol article, posted by a very astute mumsnetter years ago, comparing it to the mental 'stutter' you get when doing the Stroop test.
Ive noticed some colleages from the Philippines who have English as a second language very often use male pronouns for everyone especially in pressured situations- not because of any personal animosity or concious deliberation but because their first language does not use gendered pronouns and so the fluency of the shift between sex based pronouns doesn't come as naturally to them. Discussing it with some of them, it takes not only understanding of the grammar rules but also an extra mental step to remember how and when to use it.
I'm also an adult learner of a second language (I count as 'fluent' eg I use my second language every day dealing with the public, have passed the required immigration and work permit certification exams to the highest level) and recognise the problem - it still takes a lot of conscious effort to remember all grammatical rules, sentence constructions, verb forms, formal and informal pronoun rules, and use them correctly while also understanding and responding to the person and situation in front of you when its not your mother tounge- its certainly not impossible but theres definitely extra mental load, especially when learning, and to be honest this makes me very forgiving of language slip ups and errors. There are always social and emotional consequences of speaking imperfectly/inappropriately/being judged or scolded/feeling that you have caused offense when learning a language and interacting with the cultural and social rules of another society.
Unfortunately this is apparently the end game with insisting on the use of dissonant pronouns, like in the OP, where not using the prescribed pronouns about a third person could have no consequences for that third person who would never hear or know of it without being informed by those having the conversation. So in this context the policing of the language becomes about something else, not offense but alliance and social power, signalling compliance to a particular political ideology, signalling conformity, and as an act of social dominance from the person doing the correction/shaming/criticism.
Its worth reading the Vaclav Havel essay 'The Power of the Powerless
'Individuals need not believe all these mystifications, but they must behave as though they did, or they must at least tolerate them in silence, or get along well with those who work with them. For this reason, however, they must live within a lie. They need not accept the lie. It is enough for them to have accepted their life with it and in it. For by this very fact, individuals confirm the system, fulfill the system, make the system, are the system.'