Some important points have been missed by everyone.
An EASA license issued after 01/01/21 will not have the automatic right to a UK Part FCL license and will have to retake all exams and flight tests to obtain a UK Part FCL license (under the current agreements). Like wise a UK Part FCL license can no longer be change of SOLI to an EASA license, it will have to be converted with Exams and flight test.
Easyjet have I believe 60 percent of the fleet on the G Reg based in the UK. The UK two year validation of EASA license only applies to license issued before 01/01/21 and the validation ceases to be valid after 2022. So after 2022 as it stands at the moment to fly G Reg will require a UK Part FCL license.
On top of that the chances of getting a visa to fly for an EU carrier will be next to zero in the next few years due to a surplus of pilots in the EU, and even when the UK was in EASA there were far more mainland EU pilots flying in the UK, than UK pilots flying in the mainland EU. Language fluency requirements of most mainland EU operators stopped UK Pilots working for those carriers anyway.
As a UK national he/she/whatever they identify as won't have the right to work in EU, so other than Ryanair an EASA license wont be that useful. Even working for Ryanair they will be limited to UK or an Irish base.
There are schools that allow you to train for both the UK and the EASA license side by side (FTA at Shoreham), that is probably the best option to go for, it involves sitting the exams twice (UK and EASA).