A few YouTubers who pronounce it wrong are not evidence of widespread change in usage.
Agree completely. But it very well could be the
cause of a widespread change in usage.
If big name, high-follower-count YouTubers like Veritasium, Mark Rober, Dave Jones

, etc. suddenly started pronouncing it "soll-der," I think you might start to see that pronunciation being used by other people as well. (This would be a really interesting thesis / dissertation topic, by the way .... )
Change in usage happens more quickly than some might think. I'm not that old, but I've seen
many changes in English and German usage during my own lifetime, and I have to believe that the Internet, and in particular YouTube, are accelerating the rate of change in language.