Only people with very powerful computers like i7 or i9 who don't have lag
if your computer isn't powerful enough your FPS will drop when there are too many people around you 90 to 100+ it's normal because the CPU can't handle too many trucks with lots of modifications Also if the GPU isn't powerful enough you will have low FPS.
for the second question everyone has that graphics glitch it's still not fixed yet people started having it since update 1.30