As someone who pays for YouTube, I don't understand why I can't disable shorts fully. They already have my money. What more do they want?
The best thing you can do is stop paying and wean yourself off YouTube. It’s terrible for your mental health.
Choosing edifying content requires, of course, some caution. Avoid individual “content creators” who might feel pressure to slowly conform their content to the algorithm and sponsors’ demands. Instead, follow e.g. local arts organizations who do their events as part of a whole offline ecosystem, and then just upload video of it to YouTube. Or universities who create teaching content for their own needs but then upload it to YouTube, etc.