What causes my mcu to blow up when hooking up with oscilloscope?
You most likely have a ground issue on your board (non-continuous ground that is linked through the MCU) or somewhat connected the ground of the scope where it shouldn't be.

Your PC is most certainly grounded (sometimes, for laptops, it can be grounded in unintuitive ways through an external screen and through HDMI cables for example).

Your scope and computer are likely not connected to the same socket, you can be on a different line and thus have a voltage difference between the grounds which is probably caused by induced voltage.

This happened to me 2 weeks ago, as I found out that the ground between 2 adjacent sockets in my office had 100 V difference! My board was connected to my laptop (grounded through the screen) and a scope on another socket. Screen went black, it almost killed my laptop and my electronics, trying to understand when I finally went to measure the earth line on the sockets.