I have always had notifications of new mail regardless of which folder they were filtered into with the exception of junk/spam. That is the standard and default in Thunderbird.

So I think you must have been using an addon extension in order to get a very specific request just on Inbox.

Did you use this : Mailbox Alert 0.30 by Tjebbe Mailbox Alert allows you to specify, for each seperate mail folder, a message, sound and/or a system command that will be executed when new mail is found there. ... Works with Thunderbird 102.0 - 102.*

REgarding getting it to work in more recent version - It looks like the author has decided a complete rewrite is a lot of time and effort and therefore a significant cost to the author which is just not tenable.

I found this: https://github.com/tjeb/Mailbox-Alert/issues/76

Looked around for you and found this addon extension:

• https://addons.thunderbird.net/en-US/thunderbird/addon/filtaquilla/

FiltaQuilla 4.1 by R Kent James, Realraven (Axel Grude)

Adds many new mail filter actions - launch a file, suppress notification, remove star or tag, mark replied or unread, copy as "read", append text to subject.

Works with Thunderbird 112.0 - 128.*

I've not tested it, but it has a 'do not notify' option .

If you use addons please support the author with donations, it takes a lot of time effort and skill to write and importantly maintain programs.

I know this is a bit older (2012) but this setting has been around until recently:

https://askubuntu.com/questions/112622/how-do-i-get-thunderbird-to-give-notifications-for-only-my-inbox

"Show in the messaging menu" > change radio from "For messages in all folders" to "Only for messages in my Inbox folder"

I have not added any add-ons to Thunderbird since the calendar integration started to work without the Lightning add-on.

No that is a lot older. 12 years ago in 2012 and as the discussion you link to says, it was added by an addon. One that is not available on the Thunderbird addons web site. It was as I understand it written by someone from canonical and as they left unity in the dust for gnome so to they left the addon.

There is discussion here https://thunderbird.topicbox.com/groups/addons/T67d58466f3ab58c2 and a bug report here https://bugzilla.mozilla.org/show_bug.cgi?id=1599924 which was closed 5 years ago as invalid.

I suggest you make a suggestion for a new feature at connect.mozilla.org is you want someone to consider making a general option available, rather than one added by an addon included in some Linux distributions that used the canonical Ubuntu repository