I still don’t like the main characters. Mainly because this turn around in Personality i...

Preach

He is not trying to fix their relationship with a baby, he is trying to tie her down because he think she'll eventually run away from him because he recognize he is an asshole.
Writing wise it's to give him a reason to stop drugs and alcohol, because he realistically have no reason to do so just for Ingrid or if he isn't desperate.
Those kind of tropes usually end up with the love interest (here Ingrid) finding out about the scheme, both talking it out and then depending on the author taste...
Either the love interest will laugh at the whole thing, reassure them of their love and tell they would have accepted if asked about it anyway or they'll get mad because they feel betrayed (righteously so) even though they would have been on board if asked normally.

Ingrid seems the kind to go with the first option, but it would be interesting for her character to get mad about it.

I think you’re trying to say Emotional manipulation. Trying to “tie her down” with a baby is literally trying to “fix” a relationship. If he recognizes he’s an ass then he should just try to be better. Bringing another life into the world is not how you do that. People Try do that kind of shit all the time. “Oh, he’s a good man deep down, he will stay with me if I have his baby. She will change if he has a reason to stay.” No. No no no. It’s like, entrapment. The only thing it’ll do is make the other party resent you. Especially, if one party didn’t want the child in the first place.

No, trying to fix a relationship is when you try to make it work by working on the part that doesn't work. You said it yourself, a baby doesn't do that. And he said it himself, he just want the baby to tie her to him.
The reason why he do that is because he think of himself as a lost cause and he have no idea what to do to keep her with him. Is it right ? No. Is it actually the thing to do ? No. But he is a character that never cared about others and never learned how to treat people right. So that's a logical way of thinking for him.
The story never tried to show his actions as good or righteous so I don't know why you are so triggered by this plot point when it's obvious he won't be able to complete his scheme.

This.