I won't cite, but only because i don't have a way to index my personal PDF repository, but the common consensus among people who study such things is that anyone living above the 20th parallel (or below, technically) absolutely must supplement vitamin D3, as even a full day in the sun naked is not enough to synthesize the amount of D3 we need.
So with that in mind, I'd honestly expect more people to know this and be supplementing D3. I don't have any specific recommendations, but i do know some guidelines and recent discoveries into "max dosing", so here they are. Anecdotally, i take 5000-6000iu every two days. I have a weird sleeping schedule so i really only notice "a day" as the sort of fog and fatigue i get after having gone more than 30 hours without D3. Prior to about 2015 or so, the max dosage was in the sub-5000iu range, with most supplement's labels stating that 500-1000iu was the "RDA" for D3.
However since covid was exponentially responsible for research into literally anything that could help alleviate symptoms/the disease and accelerate the time to recovery, some doctors were giving extremely high iu, up to 250,000iu over the course of a few days, or single doses of 50,000-80,000iu, with no deleterious effects reported.
Personally, unless i actually get sick, i try to stay under 8000-10000iu, at least until someone does a longitudinal study about the long term effects of doses higher than that.
As to the article and your point about lights helping - i've never noticed anything about any sort of light. I can feel awful at noon on a clear day while outside, or awful inside under every light type imaginable. I'm glad that light (and types of lights) help some people. I just think that the root cause is D3 deficiency, and no amount of 20k lumen arrays is really going to help.
As a quick aside, if you want to supplement children with D3 i recommend finding chewable d3 or a childrens multi-vitamin with omega-3/6 fatty acids. A couple of studies (with decent N and correlations) showed that merely supplementing omegas in children's diets improved the relationship and overall wellbeing of the children's parents - you read me right, parents didn't have to supplement to get the benefits of the children supplementing.