Since there were issues raised with the NeoPixel strip I chickened out and scaled back to something more modest - an old PC fan for a load. One experiment at a time! I slightly modified the blink sketch to cycle the output by adding an input, which when grounded stops the cycling, another which keeps the output on and by adding a separate output for an external LED as indicator.
Anyhow, I’m using the high-side switch configuration (fig. 6 in datasheet) and an IRF510N at the moment. Fan power is from a 12V wall wart. I've had it running several hours now and it seems OK.
YT link to show operation if interested - SAM 0410 - YouTube