Since the Brexit transition period ended on 31st December, freedom of movement for living and working between the UK and EU has ended. This means that any UK national wishing to carry out work in the EU is likely to require a work visa.
Each country has different requirements or concessions with regard to work, so you should consult the gov.uk website for information about your particular country of interest and also allow plenty of time for the visa application process to be completed prior to their departure from the UK. You should also check that your insurance coverage is still valid for the country you intend to work in.
