What we ended up doing: download a few dozen videos from the channels we think are good for kids. I hate CocoMelon’s fast-paced videos, but find SuperSimpleSongs agreeable, so we now have a Jellyfin section for toddler videos that teach him something.
Screen time in general is highly advised against, but for that odd moment where we need extra entertainment, at least he’s watching something we’ve vetted. YouTube Kids is a cesspool of content, and your ability to block bad channels is ineffective since they pop up like moles.