Opening Training Software

Noob here, and and this is my first post. Sorry if it's in the wrong forum.

I want to find software or a website that will allow me to manually enter a number of variations of a single opening and save. (I don't have a file to upload...I would do this "over the board".)

Then I want to make my first move and let the computer play the lines I've entered against me RANDOMLY so that I'm forced to learn/recognize/remember what my best move is regardless of which line the computer throws at me.

Any recommendations? TIA.

Hmm. It seems like you just want to learn how to program a chess engine's opening book.

And then load it and have a chess engine use it.

https://www.chessprogramming.org/Opening_Book

FWIW, I eventually decided that Aimchess has an opening trainer that gets me where I want to go.

As W, I play my first move, and Aimchess responds with one of the top responses. Then I play my second move, etc. Once I have reached the end of my "book" knowledge, Aimchess lets me know how I did. I can try that line again or tell Aimchess to do something different against my opening. As B, I can choose my response to whatever Aimchess decides to play as W. It doesn't choose the same opening everytime.

All this feels like a real game...it just doesn't go beyond the number of moves that I preset. Over and over and over...