Open the error console (Ctrl+Shift+J) (make sure Thunderbird is active and has focus the same keystrokes will open I have no idea what unless it is keystrokes going to Thunderbird) Clear the console by clicking on the trashcan icon on its toolbar Click on one of the links. What appears in the error console when you click? (I am hoping something illuminating) You can right click the console entry, copy and paste it into a reply here on the forum to share what it shows.

You might also want to have a look here just to make sure things like a system browser are set. https://support.mozilla.org/en-US/kb/hyperlinks-in-messages-not-working#w_check-that-the-operating-systems-default-browser-is-specified

Thank you Matt - unfortunately I get zero errors (or even notifications) in the error console when clicking a link :/ However after trying that - closing the error console, then opening the error console back up I did see this error:

NotFoundError: No such JSProcessActor 'BrowserToolboxDevToolsProcess'

Not sure if it is related?

probably not... I would guess the issue will be in the default system browser in Windows.

One "test" is to right click the link and select save, save it to the desktop and double click on it there. What happens?

The previous error is bc of this it seems:

The error NotFoundError: No such JSProcessActor 'BrowserToolboxDevToolsProcess' is a Firefox/Thunderbird bug occurring when DevTools attempts to load while a content process is being destroyed, resulting in a race condition.

Saving the link to desktop works fine - I can click and access the link no problem. So this would seem to point to TB itself yes?

Next step is restart Thunderbird from the help menu in troubleshooting mode. Continue witn prompted and try the link.

All Thunderbird does internally with a link normally is dump it on the operating system to do something with. When it does not work it is usually another outside source that is the problem, an addon or theme can be the problem and that is what the troubleshooting step is checking. it is possible is a specific action/help application is specified in setting for links that that can be where things go wrong. But none of those tings should be present in a new install with Defender as antivirus

There can also be a number of hidden thunderbird preferences that can affect links. They are discussed in the article I linked to earlier.

Thanks Matt - Initially restart in troubleshooting mode with everything disabled and default doesn't' yield a solution - links still do not work (but it did restart in dark mode for some reason?).

Can you confirm the link you are referring to please? I just need to do a deeper dive like you said.

https://support.mozilla.org/en-US/kb/hyperlinks-in-messages-not-working

without the internal jump