Common Binary Puzzle mistakes
The usual miss is three identical symbols in a line. Two 0s already sitting together need 1s on the open sides. An empty cell between two 0s is a 1. The same is true for 1s.
Another miss is overfilling a half. On 6×6 a line may hold only three 0s and three 1s. If it already has three 0s, the leftover cells are 1s — even when that feels tight.
Rows must all be different, and columns must all be different. A finish that copies another line is wrong, even if the counts look fine.
Do not guess. If two fills both look possible, you have not used a rule yet. Look again for a half that is done, or for two identical symbols that would make three.