RE #3: Never in my time in chemistry, physics or biology courses in high school and in college, plus never in my time while working in the plant and in a lab at a pharmaceutical company, have I come across "filtrate" being used as a verb. It's always "filtered." Water, light, and data are "filtered," not filtrated.
There may be some small group of highly specialized folks who make some sort of distinction using filtrate, but they must be few and far between.
A bit of a summary of (plus some additions to) the linked thread from #4: M-W lists "filtrate" only as a noun. AHD includes it as a verb with no particular comment other than defining it as "to put or go through a filter."
Oxford/Lexico includes it as a verb, defining it as "filter," with the comment "rare."
Given that M-W doesn't include it as a verb while AHD does (which in a sense for me means that they cancel each other out in and odd way), I'd stick with Oxford's "rare" and basically never use "filtrate" as a verb.