I just flew in from Heathrow with Thai airways, I did self check in online and just checked my bags. Was not asked for anything at Heathrow end. When I arrived at immigration in BKk I said to then I have visa, gave them the print out which they scanned the QR code, but they didn’t have any visa stickers (like i usually get) so they just put 2 little stamps in for the 2 months. I’m kinda glad as my passport is practically full of Thailand visas 😂
I didn’t submit any for the application and was not asked to provide additional in that regard but it’s usually at the visa counter you might get that question. In which case always best to have ‘best onward ticket’ ready imo