In UK, it is very much a 'courtesy'. There is nothing written in any statute about use of pronouns, so-called 'mis-gendering' or so-called 'dead-naming'. To write such requirements in law is a breach of international human rights law
While an organisation can impose rules about courtesy that facilitate participation, compelled speech, expression or belief is a breach of international human rights law
I'm not sure that's entire true. Section 22 of the GRA makes it a criminal offence to disclose the birth gender [the Act uses 'gender', not 'sex] of someone who has a GRA. People often disbelieve me about this, so I'll quote the Act:
It is an offence for a person who has acquired protected information in an official capacity to disclose the information to any other person.
Protected information in this context means birth gender or that someone has applied for a GRA.
The criminal offence doesn't apply to people acting as private citizens, but does apply to a very wide range of people in their work - including HCPs, the police, civil servants etc.
So that's millions of people in the UK who would commit a criminal offence if they disclosed the birth 'gender' of someone with a GRA while at work. Obviously, if you use male pronouns or a male 'dead name' about someone who now identifies as female, you are effectively disclosing their birth sex. So, by the back door, millions of people are compelled in their working lives to pretend to believe that trans people have changed sex. At present, the offence is only committed if a trans person has applied for, or has, a GRA, but the principle of compelled speech is thus already part of UK statutory law.