I know this has got to be asked before... (sorry, but I can't find it)
I had one PC on my network that was able to see my RPi3, but once I got my RPi4 up-and-running it's not finding it.
I've read that there are some packages that need to be installed?
It's not such a big deal, since I now am using a 64gb SD and space isn't that tight. I even think slapping a USB3.0 drive on the RPi4 and copying them over might be faster than my wireless network. Just not as convenient.