Issue Connecting to WIN PC Over LAN (WiFi) & Finder "Connect As" Button Doesn't Open...

I have been accessing work related files from a shared WIN PC via LAN (WiFi) for over 10 years.

My iMac's never had any problem seeing it, let alone staying connected. It would show up in Finder Sidebar and all I had to do is select it to connect.

Then a few years ago it started having issues maintaining the connection after the screen saver or sleep was active. Example: I would have an AutoCAD drawing file open, working on it, but if I left and came back later after the screen saver or sleep started, AutoCAD would have problems saving or finding files (PC) because the connection was lost. Finder always automatically connected.

Then a month ago, Finder would not connect to the PC. I tried everything. We soon discovered that the PC's credentials (User ID/Password) was not correct, even though it had been connecting for years. The next issue was that the "Connect As" button would not do anything (open login window), except force it to try and connect. At some point the login window finally appeared. The User Name wasn't a "name" as thought but "Owner". I guess it changed when they set up the new PC and updated the OS, but it was still connecting after that with whatever the saved login credentials were. So I was able to finally login and connect. It also seemed to be maintaining the connection at first, but soon after started losing it as before.

Now it is not connecting again and I can't figure out how to force the "Connect As" login window to open. I have clicked on it hundreds of times and it only tries to connect and always shows "Connection Failed".

Another strange thing with Finder behavior is whenever I select "Network" under Locations in Sidebar, the selected highlight shifts to my iMac above.

I'm really at a loss with this. I've tried restarting everything multiple times, searched online for similar issues, but can't find anything to help figure out what is wrong, or what changed. It works one moment and then it doesn't and nothing changed from last Friday.