To date (end Feb 2021) divergence (this is not a definitive list) :
(1) international waste shipment – divergent waste transshipment law – EU bans plastics to non-OECD, Britain has enhanced pre-notification
(2) lead shot in fishing/hunting – EU Reach ban in/around wetlands from Feb 2023 (no announcement in Britain)
(3) carcinogen OELs – EU has further 2021 OELs (EH40 unchanged thus far)
(4) medicines licensing – Britain has ILAP launched 1st Jan – further information is here
(5) safety data sheets – EU has new Reach Annex II, one year grace (UK Reach unchanged so far)
There are other minor divergences
Additionally, and off topic, GB will not implement the latest proposed update to the EU motor insurance directive.