The main alteration in the wiki described behavior since the last post in that thread (Aug18) appears to be "In ocean biomes, drowned will only spawn at a height less than 5 blocks below sea level; this restriction does not apply to rivers."
Slabbing or lighting the bottom is effective in comparatively shallow water, but ineffective in deep water.
To actually render a volume of deep water safe the best method still appears to be a combination of:
bottom to surface+1 fences (with the top 3 layers walls to protect from lightning damage)
Setting jack-o-lanterns/sea lanterns/glowstone in a grid four apart
diagonally will protect a volume five layers high; two above to two
below the light sources, with the appearance of 7-light blocks in the
third layers centered between the lights. The grid would need to be
repeated every fifth layer to avoid any spawnable waterblocks.
[I have since hit on placing the top layer @61 (ie submerged by one block) and counting down toward the bottom which preseves the ability to jump into any part of the pool.
Some additional lights may be needed in steep areas (where Y is cahnging quickly).
The result is (as expected) quite obtrusive; assuming one had them in sufficient quanity, end rods would be considerably less so… (Zero tick chorus fruit farms fix half of that, but I am aware of now equivalent for blaze rods…)]
[The greater spacing of lights with alternate layers offset mentioned was tested and proved effective, however the savings in materials (minor) was insufficient to justify the increased complexity and time required to contruct.]
If changes since that thread went dormant have introduced a better way of spawn proofing (other than placing a matrix of cats, the potential teleporting of which make this insufficiently sure for my tastes), I would be pleased to learn of it.
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.