That space between the line numbers and vertical header does seem excessive.
I opened a few tabs, flipped on stacked tabs, and cycled through a few different themes. I couldn’t reproduce that spacing. To the left of the line numbers mostly looks like this for me (a slight variation here or there depending on the theme):
How’s it look using the default theme? After turning on Restricted mode and restarting? Other troubleshooting steps and things to try are here.