Windows 10: Telnet broken after installing KB5051974

Hi.We have two systems as part of production tester that used telnet to connect to units. After a windows installed update KB5051974, the communication no longer works, the connection cannot be established to UUT port 23. To be more precise about the installation, first the regular machine was auto-updated and stopped communicating. Installation of KB5051974 coincides with the issue starting. After that, a backup PC was brought online. It worked for a moment, but it installed some windows update for which I cannot remember the number for but was not KB5051974. It also broke the comms again. It

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Telnet Not in Default Apps

Telnet works fine from the commandline. It's enabled in Windows options, and I can run it without issue.

The problem is I can't associate it with the TELNET protocol under default apps. That's because TELNET isn't even an option that I can assign a program to. It's been removed from the list of protocols that can be assigned. Protocols like SCP, FTP, SSH
are still there, with apps assigned to each. But TELNET, which has always been there, is no longer in the list.

 

Telnet Not in Default Apps

Telnet is an app and a protocol.

I upgraded my Windows 10 from home to pro. Now telnet is not listed in the default apps by protocol; it always has been previously. FTP, SSH, and other similar protocols are all there, just not TELNET.

My work uses a web-based application to connect to remote sites via telnet, and it depends on the browser being able to fire up a telnet app when a 'telnet://' URL is encountered. This worked great until just recently, I'm assuming my home->pro update caused
this (though it could be coincidence).

Any help would be appreciated.

 

Enabling/Installing Telnet Server

See:
Windows 10: Install Telnet Client - Technipages