Android and Unicode

How do I enter a Unicode character in Gboard by entering, say, the Unicode number for that character? Is there a special Unicode keyboard that works in this way? Today, I wanted to enter a Unicode character found in ncurses, the one for a UL corner (this selection was wrong. But I still wanted to attempt entering the character). Or, perhaps, the lower left. Or the combination of UL and LL characters from ncurses. In these cases, I need to either draw a character, insert it and have it occupy a cursor place. Or, enter it using the Unicode number for that character. But there is no way to do these two things.