It was just an observation - and a guess on a the probable cause.
In my test there was no need to execute other commands.
[fh@lxqt ~]$ pacman-mirrors
Pacman-mirrors version 4.23.2
Local mirror status for stable branch
Mirror #1 OK 00:17 Austria https://mirror.easyname.at/manjaro/
After the reset described - pacman functioned as expected
[fh@lxqt ~]$ sudo pacman -Syyu
:: Synchronizing package databases...
core 143,6 KiB 756 KiB/s 00:00 [-----------------] 100%
extra 1636,8 KiB 3,61 MiB/s 00:00 [-----------------] 100%
multilib 145,5 KiB 674 KiB/s 00:00 [-----------------] 100%
:: Starting full system upgrade...
there is nothing to do