@newf522
I have got round to a Windows 10 / Gimp 2.10.34 / and IrfanView and still no squares or lines with an exported jpeg viewed with IrfanView. One caveat, it is a Win 10 virtual machine so the emulated hardware is basic.
Since other viewers are ok, your problem might be IrfanView + your Windows setup. Since that image you posted was a little strange, 1x1 resolution, next time you export a jpeg try turning all the options off. Especially the top one - Use quality settings from original image and further down Save Thumbnail A quality value of 90 to 95 is more than adequate. Might / Might-not make a difference.
I have got round to a Windows 10 / Gimp 2.10.34 / and IrfanView and still no squares or lines with an exported jpeg viewed with IrfanView. One caveat, it is a Win 10 virtual machine so the emulated hardware is basic.
Since other viewers are ok, your problem might be IrfanView + your Windows setup. Since that image you posted was a little strange, 1x1 resolution, next time you export a jpeg try turning all the options off. Especially the top one - Use quality settings from original image and further down Save Thumbnail A quality value of 90 to 95 is more than adequate. Might / Might-not make a difference.