On Tue, Sep 07 2021, Peter Münster wrote:

> With my installed version 27.2 the first example takes 9 seconds. The
> latter less than 1 second.

Now I've finally compiled Emacs from git-master:

time src/emacs -g 150x50 -Q --eval "(progn (require 'notifications) (dotimes (i 20) (notifications-notify :title \"TEST\")) (kill-emacs))"

real    0m0.505s
user    0m0.286s
sys     0m0.033s

time src/emacs -g 500x200 -Q --eval "(progn (require 'notifications) (dotimes (i 20) (notifications-notify :title \"TEST\")) (kill-emacs))"

real    0m4.287s
user    0m0.525s
sys     0m0.088s

-- 
           Peter