okay so i'm writing this post because just a few minutes ago i finally found the cause of this very obnoxious bug i've had for about a month now in blender, and i thought it'd be a good idea to post just in case someone else out there in internet-land happens to have it
for a little while ive had this really obnoxious issue where isometric mode (the numpad 5 key) would create these weird precision artifacts that would persist across pretty much everything, like this:

(the black streaks here are an inverse-hull outline, common for cel-shaded 3d models and something i use a lot; everything else though is just normal model)
for the longest time i had panicked over this being some kind of issue with my nvidia drivers (which i updated to no effect), or possibly my card, or maybe blender itself that somehow wasn't caught in testing (i only noticed the issue when 4.0 released), or maybe some other weird quirk of my exact hardware setup. i couldn't find any issues mentioning it ANYWHERE online; not on blender's issue tracker, not on any social media or forums or anything, which didn't really help much
and then just now, today, the 19th of february, at a time of day when i should probably be asleep: i finally found the cause of the problem

at some point in time, i had changed my default blender file to bump up the maximum camera clipping distance from 100m to 1,000,000m, and apparently having that value too high causes these issues
i don't know precisely why this only breaks the orthographic viewport (maybe blender does some kind of internal clamping conversion and the high cap value causes precision loss across the entire range?), or even why exactly i decided to bump it up that high (maybe i was making some huge skybox or plane and bumped it up to assist with that in the future?), but it meant one thing:
i have been in a hell of my own divising