My DTV has been approved today. I submitted via London and paid 300GBP 24 July (Saturday) and they requested additional documents on Wednesday 31st. I submitted everything they wanted the same day. They wanted my taxes, proof that I am in UK legaly (as I'm not UK national, do not own UK passport but live in UK), my portfolio links were not accepted in their system so they asked to resubmit and they wanted to see my name as a passenger on a flight ticket from UK to Thailand.
So I had to book a flight ticket before I knew the result of my application.
As for the portfolio, as a content creator for youtube I just went to my youtube page and "print to PDF" the first 2 pages with my recent videos thumbnails. Same for my website as a 3D Artist. Print to PDF every page of my website. Then combine all pages into single PDF and make sure it's compressed as the limit on their system is 3MB (my PDF was over 5MB originally, 2MB after compression).
For proof of my stay in UK I have found an old email that confirm that I have a settled status here in UK and submitted that. Funny enough after I submitted everything I actually read that email in full and at the bottom it said that this document CANNOT be used to prove my status to anybody and instead I need to generate a code on their gov UK visa website and then give the code to them instead. I expected they will reject it and request it again, but they accepted it anyway (probably did not bother to read the whole document like I didnt)
Pretty smooth, less than 1 week. 800GBP total cost with the plane ticket.