Do I need to stay in Vietnam after submitting my visa application, or can I leave?

They did this exact to see.if you still there ir left

A full scan will show that you left Vietnam already

And that will get your application rejected

Seriously you've been in the group for a year and a half, and this requirement from Vietnam is a surprise to you? It's almost blasted from the rooftops that Vietnam will want to see every page of your passport.

You failed the IQ test. Go to Cambodia

Yes, you must remain in a location served by the consulate you applied at until the process completes. As you have already left and thus will have stamps in your passport it's very likely your application will be rejected just for that.

Normally when you apply under Workation you also include a letter stating you are allowed to work remotely from Thailand and that you will have no interaction with any Thai entities or clients inside Thailand. The fact you've had to return to Thailand for meetings is also a strong indicator that the DTV is not the correct visa for you. You should probably be looking at a Non-B visa

Yes, this has been discussed many times. You need to stay in Vietnam the entire time. Even returning now might not work, as they are asking for every page of your passport (time stamp) to see if you exited Vietnam.

Your work is obviously so substantial in Thailand you qualified for a Work Permit. Work meetings actually in Thailand are not allowed under the DTV. I know in practice they occur but if it is a regular thing you are leaving yourself open. Why not have online meetings?

Yes, you’ll need to remain in the country, and the listed requirements confirm this. If you’ve already moved to Thailand that will probably be an issue for you. Work meetings are not a valid excuse since as a digital nomad you can have those meetings anywhere. And if your meeting is in Thailand, that’s a very grey area, since you cannot engage in any business or work here, even with foreigners.

As long as they don't ask u for interview

Wow

Yes. You have to stay in the country you applied the visa untill the visa process is finished. You can try to return and submit what they are asking, but it doesn't mean they will not reject.