He uses Multimedia Fusion 2 and a Lua Scripting plugin (at least, that’s what he’d been using for a long time. I don’t know if lua is compatible with the web export)
He’s also been known to use Love2D on occasion, but he’s been using MMF2 for years and he knows it so well that he just sticks with it.
He streams sometimes, and when the subject of engines is brought up, he expresses that he sticks with the engine because it’s what he knows so well, but he’s also aware that it… is a little bit old, turning 18 later this year, so he doesn’t usually recommend it as an engine. Platforms that are comparable nowadays in terms of design would be GDevelop and Construct, but Godot’s also a pretty fast development environment, though more traditional in its engine design.