What are the visa options for a UK passport holder currently in Indonesia looking to travel to Thailand?

If you put UK as your citizenship and Indonesia as your location, it probably tells you that you can't use evisa website because the Thai embassy in Indonesia isn't using the website yet. What that means is you need to go to the website and find out their process and possibly go to the embassy to apply. Either way you will have to get a physical visa placed into your passport if they're not using the new system.

The evisa system is only about a month old, so you also have the option of trying to do a Visa application by putting UK as your citizenship and UK as your location. This means you'll be applying through the UK embassy as if you were there, but since you no longer have to mail your passport in, it's theoretically possible. It's too new to know if this will work.

The issues you may run into are as follows:

They will ask you for every stamped page of your passport from the last 12 months and may notice you're not stamped out of Indonesia.

They may ask you to show a flight from UK to Thailand, but it's possible you can screenshot a "planned flight you want to take" and send them that as your travel intentions to get the visa.

You also have the option of just entering on 30 day visa exempt which you can extend inside the country for another 30 days once you arrive. This will give you 60 days inside Thailand without getting a Visa, as compared to the 90 you could get with a tourist visa (60+30).

If UK passport you can come visa exempt but need apply for Thailand Pass