Easiest/Cheapest alternative of an oscilloscope to observe PWM signal, if any
Here's a few options:

Chinese Logic Analyzer. There are knockoffs available of the &quot;Saleae logic 16&quot; for around 50 bucks on ebay. These work great for debugging digital connections. If you can afford it get the genuine one of course.

Read the signal with a microcontroller and transmit it over USB as DKNguyen suggested. The simplest would be digital read, then transmit in a loop but that might not be fast enough, in which case you might need to pack multiple samples into 1 character or something like that. You will also need to manage the timing of the samples, while simultaneously transmitting via serial, so the code won't be trivial.

Same as 2, but a better way that just occurred to me is this: Don't read and transmit simultaneously. Simply read data into an array, and once the array is full, stop sampling and transmit the captured data over serial.