My browser / operating system: ChromeOS 14541.0.0, Chrome 116.0.0.0, No Flash versions detected

i was minding my own business then i filled in something and i was like “theres no holes” so i selected a square and it was vector:

it was bitmap i turned it to vector then bitmap again then the outline became thickness 100 randomly

This happened to me:
https://scratch.mit.edu/discuss/post/7274020

Can you try turning off your extension (don't name it due to this policy)? According to your screenshot, you use 2.0 color presets, and I know that @medians does the same thing.