Rated 5 out of 5 stars

yazan: SangPhan87 tarih: Mart 22, 2024 ·

Next Unread Group not be installed because it is not compatible with TB 115.8.1 (latest version). Please update this add on.

This review is for a previous version of the add-on (1.2). 

yazan: Dillinger (Geliştirici) tarih: Mart 22, 2024 ·

It should currently work with Thunderbird up to 125.*

You can try to update or install it from within Thunderbird:
Go to the Add-ons Manager and search for Next Unread Group.