Why this happens

[n_e_k_on]

See the weather widget huh. How to solve 

[a1309]

Long press, go to settings. Enable match with dark mode

[n_e_k_on]

Okay 👌

[n_e_k_on]

This shows

[n_e_k_on]

This shows

[RαʝҽʂԋKυɱαɾ21]

JUST SELECT BLACK
AND ENABLE MATCH WITH DARK MODE

AND CHECK IT'S WORKS OR NOT

IF NOT THEN
ON DARK MODE FIRST THEN ENABLE THAT OPTION

[n_e_k_on]

Not working 😕

[RαʝҽʂԋKυɱαɾ21]

THEN YOU ARE USING OTHER THEME THAN DEFAULT

CORRECT !

[n_e_k_on]

Yeasssss

[RαʝҽʂԋKυɱαɾ21]

THEN YOU CAN'T CHANGE WIDGET TO DARK MODE !