I tried updating the NVIDIA driver both using the Lenovo Support Bridge, which failed, and then from softpedia.com, which also failed to install. Windows Update reports that everything including optional things is up-to-date.
Solved the paint.net problem by going to Paint.net's settings > Graphics > Rendering device and changing that to Intel HD Graphics 530 instead of NVIDIA GeForce 930A. Also re-enabled Use hardware acceleration. Now working OK.
