Regarding
⦻ U+29BB CIRCLE WITH SUPERIMPOSED X,
there also should be a
SQUARE WITH SUPERIMPOSED X
as seen in map legends representing electrical towers.
Yes there are many Unicodes with X's in boxes,

$ unicode --max 0 --brief -r BOX.*X 
☒ U+2612 BALLOT BOX WITH X
⮽ U+2BBD BALLOT BOX WITH LIGHT X
🗵 U+1F5F5 BALLOT BOX WITH SCRIPT X
🗷 U+1F5F7 BALLOT BOX WITH BOLD SCRIPT X
(and plenty others)

but none where the X exceeds the square!