Are "Round the world" flight tickets still a thing?

In fairness, three months is nothing like long enough to make this worthwhile. Get a cheap flight to the Far East (there was a thread the other day about bargains to Bangkok) and explore the region: flights on Air Asia are absurdly cheap if booked a couple of weeks in advance.

RTW tickets are still a thing but they aren't always the best value. With the growth of budget airlines it can be cheaper (and more flexible) to book flights separately.

What the RTW travel sites (e.g. https://www.statravel.co.uk/round-the-world-travel.htm and https://www.trailfinders.com/around-the-world) are good for is suggesting possible routes - though I would agree that 3 months really isn't enough. To go around the globe properly you would need at least 6-9 months a preferably a year.

If I was fortunate enough to have 3 months free then I would just book a return to Bangkok and then follow my nose around SE Asia for 12 weeks.

The first thing to think of is a realistic budget. For example, 3 months at £50 a day doesn't sound like much to pay for everything but over 90 days it comes to £4500 in total. I've met plenty of young people on my travels who had dreams of going around the world for a couple of grand but had blown all of their money in the first 2 weeks so had to either go back home or plead for some extra funds from the Bank of Mum and Dad.