Is it okay to cast off for neckline near crosses (cables)?
Looking at the photo of the front, there is a crossing in the cable just two rows below the cast off/pick up for the neck.

I would go with the pattern, and see how the stitches work out in the casting off.
When you see them pulling so much that you do not like it you can unpick that bit of casting off, drop all the stitches of the cable, let them run down to just below that last cross and pick them up in knit without the twist. A crochet needle and a (short) cable needle will make the picking up easier.

Alternatively, you can just forget to make that last crossing, (not following the pattern,) but do so on both sides of the front and/or back, not just on the left or on the right (easy mistake to make.)
You can make the last crossing on the front but not on the back, if you think that is best.