These "dots appearing only while (not) focused" are known as "extinction illusions", namely

    "25 - Appearing Dots"

is "McAnany's type" [1], and

    "26 - Disappearing Dots"

is known as "Ninio's type" [2], according Akiyoshi Kitaoka's materials. (I have recreated them too few years ago [3][4], before getting to the source.)

[1] https://www.psy.ritsumei.ac.jp/akitaoka/kieru3e.html#:~:text...

[2] https://www.psy.ritsumei.ac.jp/akitaoka/kieru3e.html#:~:text...

[3] https://codepen.io/myf/full/XjdmJy ( scintillation warning)

[4] https://codepen.io/myf/full/jMqoMW ( scintillation warning)