1. Again I have two computers, John-PC1 (mine), and my wife's, which is John-PC. Thus, on John-PC1, in the credentials box, do I enter John-PC, plus the user name and password for that computer? Somehow, this does not make sense to me, but I am not a network user; it would seem that if my supposition is correct, and if there are at least three computers on the network, I could only access one of them.
2. Just found out that the printer, which is set up as Wi-Fi, prints from both computers. Its software is on John-PC1, but on John-PC, the Windows 10 update removed the marking as the default printer.
Hmm, that first statement cannot be accurate, there has to be at least a partial software installation on John-PC, else I could not have marked it as the default. It has been a few years since I set up the printer, but I do recall that once in a while, John-PC installs something for the printer by itself when a problem has arisen.
3. Yes, both John-PC1 and John-PC show up in File Manager/Networks (at least when I remember to wake up John-PC, the user thereof being away teaching school.
4. One thing I have read, including a few minutes ago is that if, in network settings, you disable the use of passwords, you ought not need to worry about credentials. I disabled that setting on both machines yesterday, to no avail.
5. No list of the changes I have made, but I am sure that they were all in the use of Share in File Manager and elsewhere;. That does not seem to me to have any bearing on this credentials problem.
6. I recall seeing that both machines are on the private network, which is the only one I have. Were that no correct, could John-PC print? Does it not use that network to send the print command via wi-fi to the printer? Printing on John-PC1 worked as soon as the Win10 update was complete, so obviously it was still marked as the default printer.
7. Working backwards (I am good at that...), am I even close on my number 1 supra?