Google provides a bit of info on this. Try "sunspot cycle 17 WW2". There is the story of east coast US being able to receive Rommel's North African tank communications but have seen no hard evidence.
Solar cycle 17 peaked in 1938 and had bottomed out by 1944. There were flares though that did have strong effects.
https://eos.org/features/the-geomagn...september-1941
There are reports of the wireless intercept station near Winterpeg receiving both German & Japanese sigs.