Starting QGIS on Tumbleweed 20210904 I see in the log:

2021-09-13T10:25:53     CRITICAL    Problem with SAGA installation: SAGA was
not found or is not correctly installed

QGIS is working fine but this is not nice.

I did install saga (sudo zypper in saga-gis), restarted QGIS and problem gone.

Then checked the install package:

$ sudo zypper info --requires qgis | grep saga
<empty>
$ sudo zypper info --suggests qgis | grep saga
<empty>

That explains why it was not installed when installing QGIS.

Can the dependencies of QGIS be updated so that also SAGA is installed?