The UK officially left the EU on 31 January 2020, however there will be a transition period until the end of 2020, meaning that the existing rules on travel, for the UK and EU will continue to apply until 31 December.
If you are travelling between the EU and the UK for conferences and events, it is recommended that you keep yourself informed of official advice.
Additional sources of information for your convenience:
British Government: Department for Transport live website
British Government: The Transition Period live website