The 7" Video Assist 4K doesn’t have a still function either, unfortunately.
I generally record 10 second to 10 minute sessions, and if I want stills from a particular moment, I use ffmpeg to spit out individual frames for a whole second or two of video around the point of interest, so I can pick out my favorite(s). Even on a relatively stable image on a clean-power system, the edges/noise often vary a lot from frame to frame.
For example, this uses the -ss option to seek to a specific time, -frames:v to output individual frames, and a format code in the output file name so the files are numbered consecutively.
ffmpeg -ss 01:05.50 -i Capture0001.mov -frames:v 30 frame%02d.png