李永乐 is a science teacher who has published a large number of science lectures/lessons on YouTube. Each lesson covers a specific topic, some harder than others, but all aimed at native speakers. You need either fairly good listening or reading skills, or time and energy to work on each episode, but the content is overall clear and with a logical structure. Each episode also has subtitles, which makes it easy to pause and check the subtitles more closely.
The channel covers a broad range of topics, including physics, chemistry and mathematics. Some videos answer interesting questions, whereas others focus more on basic science.
HT: u/takethetunnel on Reddit for recommending this channel.