How do I find the character on the cover of the new update? that is totally white

Besides what are the monster girls that I can have sex with I can not get any other besides these Spider, Slime, Cat, Ice Harpy and Harpy small

I would like to activate a guide in the game or something of the genre to fill my doubts when I need it as if I had said which woman contains a sex scene or location of items, puzzle tips

After you're far enough with Mai's events two shrine maidens will appear in front of the castle in Aldlyn. The girl from the title screen is one of them.

If you mean Thunderkitties with cat. then you have them all. But the others will get their scenes as well eventually. :)

The walkthrough will get more detailed, and some information about monstergirls is planned to get added in a monstergirl encyclopedia eventually. But obviously not everything will be explained in full details in-game, that's what the walkthrough is for.