What happens to a DTV visa if a second visa type like the LTR is approved?

Cancel the DTV , leave apply for non-I’m B or LTR

The DTV Will be cancelled and you'll get the LTR instead, no major issues, the company should help in the process.

Nothing happens as you won't be issued a 2nd visa in that way. You need to attend immigration and apply to change your visa from one type to the other. I assume the BOI can advise you on how to do this since they are the ones that issue LTR visas

The company should be helping you with any potential visa switch. One of the questions you might want to ask them is how well versed they are with dealing with that. If they have a competent HR department that is used to helping new starters get the correct visa and work permit, then that would be a plus. Presumably there will be a process, like a number of meetings with them rather than one interview then 'ok you start on Monday' so I would try to schedule one of those meetings/interviews with the relevant HR staff there so that they can talk you through the process.

You will just move over to the LTR and DTV will be cancelled. LTR is a better visa anyway. Congrats on the job. Is it 17% flat tax rate too? PS: I do not know about transferring visa in country or if you have to apply outside for LTR. When I went from my retirement to visa exempt for BOI I had to get my initial B visa from Singapore. Hopefully you can get it all done in country. I did not mind my trip to SG though. Five nights paid for in a 5* hotel and met up with old pals as I had worked there.