The latest release of QSWAT+, version 3.2.2, works with QGIS 4 as well
as QGIS 3. You can find it at
https://github.com/swat-model/QSWATPlus/releases.
It is functionally the same as the previous release 3.2.1 so there is no
need to update unless you want to use QGIS 4.
My thanks to Celray James Chawanda for doing most of the work on this.
Chris