My Win10 laptop can't see my Win10 desktop printer

On the computer that can see everything, look at the settings under Settings/Network and Sharing/Network and Sharing Center/Advance Sharing. Copy these settings to the other devices. Make sure all Computer devices are on a Private Network, not Public. Turn on Network Discovery, File and Print Sharing etc and make all of your computer devices the same.
As for the Printer, go to Settings/Devices/Printers and Scanners right click the Printer and make sure it is Shared. Give Full control to Everybody.
Then press the Windows key+R and type sysdm.cpl and press Enter. Press the Change button to rename computer and make sure all computers are part of a Network you Name, (ie) Home or something, not the generic Workgroup. Apply and OK and restart all the computers.

Have you tried:

• Control Panel > Devices and Printers
• Add a Printer
• Click "The Printer I Want Isn't Listed" to stop search
• Choose: Select a Shared Printer By Name
• Now enter the path to the printer : \\sharedcomputername\\sharedprintername
• Next

OK, First some basics.
The PC the printer is connected to is a desktop. Is the printer connected by USB?
The problem PC - is this a desktop or a laptop?
Lets call the printer PC the MAIN PC, and the problem PC the NEW PC.

In the meantime,
In File Explorer, under Network, can you see MAIN PC on the NEW PC?
Can you see NEW PC on the MAIN PC?

Also: do both PCs have the same WORKGROUP?

Can you describe the connectivity? Wireless or Ethernet? Best to describe the whole setup of all 4 PCs.

So lets try this too:
Make sure all 4 PCs are on the same WORKGROUP.
Turn off all 4 PCs (completely off).
Turn off your wireless router. Wait at least 30 seconds. Turn it back on. Wait for it to fully initialize.
Now, start turning on the PCs one at a time. Wait a minute or two for each one and check to see if it shows up in the Network section of Windows Explorer (File Manager) on the first PC you start.
If all goes well, all 4 PCs should show. If they don't then you may have a networking problem.

If the laptop sees the MAIN PC, and vice-versa (in Windows Explorer), then try to Add a printer again.
Report back what you find or don't find. Everything is a clue!

So what I am thinking is that the router is now completely lost. It is trying to keep track of these machines according to networking logic.
That's why if you systematically make the changes as I described above, I would expect the router to recognize that all these machines are in the same Workgroup and can talk to each other.

Also: You can name the Workgroup anything you want, not just WORKGROUP. You could name the workgroup gwandless if you wanted.