Any Dpm sheet over older then 1990 I wouldn’t risk going over it without a liquid Dpm as it will be perished in places.
you don’t but any primer under a liquid Dpm unless it’s a epoxy primer. Go with ardex DPM1c or Fball F77
You need a super smooth surface to bond to. A cement screed isn’t good enough and imperfections will show through the LVT. Needs to be on 3mm minimum. You need a A2 notch trowel as well to glue it.
How long has the screed been down ?
If glue down ( dryback ) LVT
No , you need to put a smoothing compound down.
If Click LVT you should be ok. Needs a moisture test in the slab 1st though.
Looks like the chipboard is rotten.
You need to get all the old flooring up and out and let the chipboard dry out by letting it breathe.
Then see how much of that needs replacing.
You need to sort them all out and stack them flat. You will then have to glue the edges together as a lot of the locking system will be damaged. You will need a flat sub floor to put them over as well.