I get burnout. In high school, when I took French, the teacher called it “reaching your saturation point and she’d stop the lesson before the class was over because she didn’t want the students drilling in the language lessons beyon theire saturation point, beyond when they’d had too much.
In writihing, I reach my saturation point after 40 minutes to an hour. When I get to that point, I save what I’ve written and do something else. Then I go back to my writing after a while when I’ve recovered.
I like the “Chunky Method” of writing where you write in chunks. That describes what I do . I write in time “chunk.” I stop when I feel myself getting worn out and take a break before goiing back to writing again latter.