1.17.1, 21w39a, 21w42a, 21w43a, 1.18 Pre-release 1, 1.18 Release Candidate 1, 1.18 Release Candidate 3, 1.18 Release Candidate 4, 1.18, 1.18.1
Lightning (using /summon command) 'de-ages' the oxidized copper block it hits fully and also some surrounding blocks a few oxidization levels but that does not happen when the lightning hits a block that is waxed.
Lightning obviously would not de-age the waxed block itself but the non-waxed surrounding blocks should still be affected by it.
None of the blocks got de-aged, even though it did set fire on the surrounding blocks.
1. Create 2 copper block testing areas. I'm using 7x7 ones.
2. First test - summon lightning by standing on the non-waxed block
3. Notice that the block itself will fully de-age and some blocks around it will de-age some levels.
4. Second test - Try summoning lightning by standing on a waxed block.
5. Notice that the waxed block would not de-age (intended) but any other blocks around it don't de-age either.
These waxed blocks can also create a sort of occlusion (See Photo) where if you summon lightning on either side, the waxed copper blocks in the middle would not let the de-aging effect of lightning pass to the other side.
Code analysis can be found in this comment.