A few thoughts on subjects that haven't been touched on a ton or framing which might help you understand some of the points you've brought up:

• I think it's important to note up at the top that all words are made up and definitions are merely attempts at society to agree on what a word means so that we can communicate with each other. The presence of slang, the creation of new words, and the shift of the definitions of words over time are all important factors when we talk about the deep specifics of a particular topic or idea.
• Nearly everything in this thread is about a topic which broadly falls into the category of "loosely defined social concepts" more formally known as social constructs. Examples of loosely defined social concepts include: gender, romance, beauty, family, race, wealth, trendiness, class, art, and status.
• Social constructs exist on a spectrum, with some having stricter definitions. For example, dictionaries exist in languages because additional structure is useful. Currency is often defined by governments to help more directly understand wealth or money so that individuals can exchange on equal terms and so that individuals can be taxed.
• Sex and gender used to be interchangeable words in western society, back before we understood any "modern" science which delineated the two.
• Over time sex became a legal and medical term, to describe people who were assigned female at birth generally by genital inspection of the doctor or whatever was recorded on the birth certificate
• Gender theory, or at least the modern roots of it, emerged during women's suffrage in the united states as a way to separate the social factors from the biological ones - to provide framing to examine social pressures, social norms, social ideas as a construct and not innately biological
• Modern gender theory importantly separates gender identity from gender expression. Much of the discussion in this thread about gender nonconforming individuals such as tomboys being different from trans masc individuals comes down to this framing and their assigned sex at birth. Strictly speaking, having a gender identity which does not match the assigned sex at birth can be considered trans. I say "can be" because labels should never be forced on someone else
• Labels are personal, and therefore messy, and do not always neatly match with definitions for words that are in dictionaries or generally accepted in whatever social circles. For example, a person who has a gender identity of non-binary, who presents very feminine, could still identify as a transmasc individual as an explicit recognition of their internal sense of gender or the steps of transitioning they may have taken.
• Titles and pronouns and honorifics are individual preference and are not strictly gendered. Take, for example, the historical use of words such as lord, king, grace, duke, doctor, baron, viscount, jester, chief, lieutenant, esquire, the honorable, elder, sensei, the wise, acolyte, apprentice, etc. - these are used to signify a specific role in society or someone's personal preference. Unsurprisingly, people can often have feelings about the use of these words
• If you or someone you know happens to have a nickname or another name they go by in certain contexts or overall, it might help to reflect upon these names and the reason they are used. In some cases, they are forced upon people and undesirable, such as nicknames that come from hazing or bullying. In other cases they are adopted for any number of reasons, including that the person just doesn't like their name or prefers this one. Think about how the person who uses or has these names used on them feels about their usage - this same framing can be used when it comes to pronouns or just general perception by others in a society.
• A lot of the framing in this thread is on the gender binary, or genders created out of the sex binary (importantly, not a true binary in any science... nature is messy). Attempts to understand non-binary individuals through a binary lens will necessarily fall flat as these individuals do not see themselves as existing within the binary.
• Gender identities which are non-binary are often based on one's gender identity - which is also a loosely defined word. A sense of self ultimately likely comes from feelings, and just like some people feel strongly that being a mechanic is a masculine trait, people might feel that literally anything is gendered and their gender identity is composed of those feelings. Thus even things which binary folks don't generally consider to be gendered may be an important part of one's sense of their non-binaryness.