Is there a mandatory work period in the UK after graduation for work purposes, not PR for a Master's?

No, there is no mandatory work period you must complete in the UK after graduation. After finishing your master's, you can apply for the Graduate Visa, which allows you to stay and work or look for work for up to 18 months (if applying from 1 January 2027 onwards).

You are free to work in any job or be self-employed during this time, but you are not obligated to work for a specific period or employer. This visa is designed to give you flexibility to gain work experience, not a compulsory work duration.