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It seems the latest Windows Updates broke the URL protocol handlers again. What are others doing to try and work around this issue? I've tried reinstalling the Windows Integration Pack as well as adding the needed registry keys again.

yes possibly reinstalling the client pack should help.

Tried that, no luck. Seems like telnet protocol handler lost its last leg in Windows 11. I may try the HTML console, but, in the past, it is very limiting, particularly when trying to paste in blocks of code. Any chance on moving to a protocol allowed by Windows 11? Even if I could somehow get telnet to work again, a future Windows update will surely break it again.

You can force firefox to use whatever you need
https://github.com/SmartFinn/eve-ng-integration
steps 5-6

Interesting. I was experimenting with a bunch of the reghacks for URL handlers to work on a laptop. Apparently something worked to allow Firefox to work with Putty. Edge or Chrome fails. This is a corporate environment with Windows desktops. I'll try my main desktop once I get to a place where I have the opportunity to implement reghacks and reboot. Currently it fails with Firefox as well. But it is configured to use SecureCRT.
Thanks!

So, with Firefox, it appears the following reghacks will allow Putty to work as the telnet protocol handler.
This worked on two Windows 11 clients.
One client, Chrome and Edge also worked after the import and reboot.

Windows Registry Editor Version 5.00

; --- Register PuTTY as an App Path ---
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\putty.exe]
@="C:\\Program Files\\PuTTY\\putty.exe"
"Path"="C:\\Program Files\\PuTTY\\"

; --- Register Telnet as an App Protocol (NEW REQUIREMENT) ---
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Protocols\telnet]
"ApplicationName"="PuTTY"
"ApplicationDescription"="PuTTY Telnet Handler"
"AppPath"="C:\\Program Files\\PuTTY\\putty.exe"
"AppArguments"="-telnet %1"
"UseUrl"=dword:00000001

; --- Classic protocol handler (still required) ---
[HKEY_CLASSES_ROOT\telnet]
@="URL:Telnet Protocol"
"URL Protocol"=""

[HKEY_CLASSES_ROOT\telnet\shell]

[HKEY_CLASSES_ROOT\telnet\shell\open]

[HKEY_CLASSES_ROOT\telnet\shell\open\command]
@="\"C:\\Program Files\\PuTTY\\putty.exe\" -telnet %1"

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\System]
"EnableUnsafeProtocolHandlers"=dword:00000001

This is really odd.

Three computers, three different results. All had recent Windows Updates. This last one, my primary working computer, I could not get any browser to open telnet links with Putty or SecureCRT until I did the following: (Thanks to Gemini for this)
I'm really dreading the next update cycle.

Windows Registry Editor Version 5.00

; 1. Register the Application
[HKEY_LOCAL_MACHINE\SOFTWARE\RegisteredApplications]
"SecureCRT"="SOFTWARE\\Clients\\Telnet\\SecureCRT\\Capabilities"

; 2. Define what the application can do
[HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Telnet\SecureCRT\Capabilities\URLAssociations]
"telnet"="SecureCRT.Telnet"

; 3. Define the actual command
[HKEY_CLASSES_ROOT\SecureCRT.Telnet]
@="URL:Telnet Protocol"
"URL Protocol"=""

[HKEY_CLASSES_ROOT\SecureCRT.Telnet\shell\open\command]
@="\"C:\\Program Files\\VanDyke Software\\SecureCRT\\SecureCRT.exe\" /T /TELNET %1"