To put your screenshot on the bug report page (I'm assuming you're using windows but I think it's the same thing on mac) Click options-resource packs, then click open pack folder and press Backspace, find the screenshots folder and double click it, scroll down to the bottom to find your most recent screenshots, then go to the bug report page and find "Drop files to attach, or browse" and click and drag the screenshot to the rectangle
On some computers (mainly older laptops) the computer limits the number of keys able to be pressed in some cases. My old laptop could press fn+f3+g to show chunk borders but not fn+fn+b to show hit boxes. If you try plugging a different keyboard into the computer then that is most likely the issue. Other than that I cannot help
To put your screenshot on the bug report page (I'm assuming you're using windows but I think it's the same thing on mac) Click options-resource packs, then click open pack folder and press Backspace, find the screenshots folder and double click it, scroll down to the bottom to find your most recent screenshots, then go to the bug report page and find "Drop files to attach, or browse" and click and drag the screenshot to the rectangle
Hope this helps
Not enough information + not minecraft Java
Put this in minecraft bedrock edition with any video/audio settings possible
On some computers (mainly older laptops) the computer limits the number of keys able to be pressed in some cases. My old laptop could press fn+f3+g to show chunk borders but not fn+fn+b to show hit boxes. If you try plugging a different keyboard into the computer then that is most likely the issue. Other than that I cannot help