Questions about subfloor prepping for LVP
You will most likely need to a mix of fixes. At the edge where the piece is tilted you may simply fill that with a trowel grade floor leveler. If I am thinking correctly, that is subfloor only, not an underlayment you can pull up. The walls are sitting on the floor you see now. Modulars are built as light as possible for towing to the building site so quite possibly if you pull up the floor, you will expose the insulation and floor joists.
The gap in the first picture will definitely need sanding, and perhaps over a large enough area to lower the other side too, but take no more than 1/8&quot; or less off of the surfaces or you will weaken the subfloor too much.
The gap in the 3rd picture can be filled with floor patch as you suspect. If the floor is thick enough it may be able to span over the gap with no filler, but it would be better to fill it.
Typically each maker of laminate floor has their own &quot;flatness&quot; recommendations. It runs from 1/8&quot; over a 5&quot; span to 3/16&quot; over an 8' span and anything in between. Your last picture with the level &quot;ramped up&quot; to measure the end is not the intent of checking for flatness. The straightedge or level used as a straightedge need to be &quot;balanced&quot; over a hump or depression and the ends are checked over humps or the middle is checked over depressions. The way I see the edge at 1/2&quot;, may in reality only 1/4...
So again, sanding will be your help on some of the fixes, but do not go down to far. If there is still a dip or ridge that is too high following the before mention guideline, use trowel grade floor leveler to finish the task.