Hi,
"after a while" means: when i did use vi.
Meanwhile it is clear this was the reason. Simply starting vi in a foot
terminal, without a file, and immediately returning to the shell caused
that behaviour.
I could stop it by removing my /etc/vim/vimrc.local file.
Content of that file was
syntax off
set mouse=
set ttymouse=
This file was a relict of working with x-server it is not any more needed
with sway.
Sorry for the inconvenience,
Johann
highlights the text under the mouse-pointer which is the expected behaviour.
in a sequence 0;45;9M0;45;9m being displayed at the shell prompt.