Helpful peeps for your own stuff cos some dude called Dave asked me about it on the bus for his alternate reality My Little Pony fanfics:

On yootooob:

Artifexian

Overly Sarcastic Productions (specifically Trope Talk)

Tierzoo (for anyone inventing species)

Monsieur Z (alternate history ideas)

Alternate History / Knowledge Hub (alternate history ideas + random facts)

Hello Future Me (very world-building specific)

Terrible Writing Advice (laughs and getting the best advice around)

Writing With Jenna Moreci

Kurzgesagt (sci-fi in particular)

Betsy Lee (fun)

Lord Bung's Confinement (sad fun + gateway into SCPs)... Lord Bung's other stuff is mostly "Y hoomanz stoopid?" oriented.

Spacedock (sci-fi specifically: especially for understanding space ship design)

Ellen Brock

UniversalHeat (apocalypse juice injections)

Shadiversity (weapon realism)

Tale Foundry (myths + general writing/worldbuilding jazz)

Khonjin (quite simply the best character advice imagineable)

The Templin Institute (checking if someone stole your idea before you even came up with it + awesome monologues)

Super Science Friends (hmmm yes very good world-building advice totally)

CGP Grey (because knowledge + making everyone pro-immortality)

Your Mum