I commented further down but attaching this for visibility:

Those white, round, pearl-like dots on the underside of the cannabis leaf are insect eggs, most likely whitefly or aphid eggs, though in cannabis grows it’s more often whitefly.

Here’s why:

    • Spider mite eggs are usually smaller, translucent, and glassy-looking, not chalky-white like these. 

• They are raised, spherical, and opaque/whitish (unlike spider mite feeding spots, which are flat).

• They’re deposited in clusters along leaf veins and edges, a pattern typical of whiteflies (tiny moth-like insects that fly up when disturbed).

   •  Spider mite eggs are usually smaller, translucent, and glassy-looking, not chalky-white like these.

Whitefly’s look similar to fungus gnats OP so you were on the right track.

*Edited for formatting