Here in Australia I am surrounded by people of many different genders, and so far have not caused complaint by using they/them for everyone, regardless of gender, whether cis or trans. Plenty of others do the same, and they tend to be people wearing the rainbow flag, rather than the insensitive.

It is always best to ask and try to remember the pronouns, but often it is not possible at the time, and it is better to err on the side of caution when you don't know yet what they use. Eg: As a female, I do prefer she/her, but if someone didn't know that, then I would still prefer they/them to being persistently referred to as he/him. Males likely have a similar dislike of being referred to with the wrong pronouns, but they/them encompasses everyone in common Australian English (eg "whoever left their jumper behind, they need to go pick it up from the office") so seems the best compromise till a conversation can happen.