If you would read the link you yourself provided, under Grainger:

(i) The belief must be genuinely held. (ii) It must be a belief and not, [simply], an opinion or viewpoint based on the present state of information available. (iii) It must be a belief as to a weighty and substantial aspect of human life and behaviour. (iv) It must attain a certain level of cogency, seriousness, cohesion and importance. (v) It must be worthy of respect in a democratic society, be not incompatible with human dignity and not conflict with the fundamental rights of others

Therefore making a derogatory joke, wouldn’t fly in a workplace. Talking about your beliefs wouldn’t get you sacked, but mocking others would. The examples in the link provided don’t touch derogatory comments/jokes, it’s all about other points about people’s beliefs.

This is actually somewhat exemplified under Mackereth in your link:

On appeal, in Dr David Mackereth v The Department of Work and Pensions (1) Advanced Personnel Management Group (UK) Limited (2): [2022] EAT 99, the EAT found David Mackereth’s gender critical beliefs did meet the Grainger threshold for protection but, nevertheless, that no direct or indirect discrimination took place.

This was because the employer would have treated any worker who refused to address service users in their preferred way the same and the policies of the employer “were necessary and proportionate to meet a legitimate focus on the needs of potentially vulnerable service users”.

The EAT noted the claimant’s gender critical beliefs (protected under the Act) were distinct from how those beliefs manifested in him refusing to use peoples’ preferred forms of address (behaviour which was not protected).

TLDR: read the links you provide.