The best source I know: https://betterexplained.com/
Also plenty of youtube channels, like Numberphile (many of the featured hosts have their own channels), 3Blue1Brown, Mathologer, Wrath of Math and many more. They have vast libraries covering pretty much any topic imaginable. It’s all top tier presentation, so intersting they made me study math for fun - I’d rather watch Numberphile than Netflix.
I’m torn on this, because on one hand Slack is better, but I’ve ever only got the option to use the free tier with Alzheimer’s. Honestly, that’s so crippling I might rather suffer Teams with full history.