Just apply for the appropriate visa, make sure you have all the relevant paperwork...
My visa was approved and passport stamped within a week, flights and ASQ booked, insurance paid for, COE approved within an hour ... just need my negative covid test certificate and fit to fly which is this week. Then flying on Sunday :)
All easy and straightforward if you prep everything.
who said anything about a holiday... the OP is going to see family. Others are going back to Thailand to be with wives, children, for work, or simply because they usually live there halc the year.... so yes , lots of people travelling to Thailand.
Really not sure why you commented because UK is not stopping people from leaving UK if they have the appropriate paperwork ( visa, COE, insurance, bookings, covid test results .... )