I was searching through docs at https://www.gnu.org/software/emacs/manual/html_node/gnus/ but could not find the proper key sequence for this. What is the key sequence for this?
3.9.2 Thread Commands --------------------- ‘T k’ ‘C-M-k’ Mark all articles in the current (sub-)thread as read (‘gnus-summary-kill-thread’). If the prefix argument is positive, remove all marks instead. If the prefix argument is negative, tick articles instead.
(info "(gnus) Thread Commands")
And please do not ask me, how should you guess this without readind the manual, or why
M-u does not work on ‘process marked’ articles.