When I boot into 5.8.0-49-generic or 5.8.0-50-generic, my system literally breaks (my WiFi, touch pad, Ethernet, speakers, screen brightness adjustment, and Bluetooth don't work).
So, since then, I always boot into 5.8.0-48-generic, until a kernel release that doesn't cause bugs for my laptop.
Today, I thought that does Ubuntu automatically uninstall older kernels? So someday when I turn on the laptop, I see that there's no -48 kernel and it causes problems for me?
No. Ubuntu does not delete old kernels automatically. That's something the user has to do manually.