Among the things, a 'blue pill' (stm32f103c8) (used to) have a 10k ohm pull up resistor at D+, some PCs/laptops have trouble with that, but most others work.
And that it seemed you are trying to use DFU (roger's) boot loader.
Do you have that boot loader installed? that needs an st-link dongle
https://www.adafruit.com/product/2548
https://www.st.com/en/development-tools/st-link-v2.html
or a usb-uart dongle to install it first hand.
oh and have you tried blinking the LED?
if the LED didn't even blink then the problem is probably elsewhere than USB CDC Serial.
oh and for DFU (roger's) libmaple boot loader, it first connects in DFU mode, and later jump to your sketch, it may take a single-ended-zero (usb reset) to get it to enumerate. i.e it first connects as vid 1eaf pid 0003 the bootloader and later jumps to your sketch which should show a different VID/PID.
if you have trouble with that you may need to 'disable/enable' the device to get it to reset. in linux there is a usbreset utilityhttps://github.com/jkulesza/usbreset
if you are still having trouble with that, an advice would be to get the st-link dongle as mention above to install your sketch.
That would 'most likely work' as you won't have to deal with another usb boot loader in the same device.