Here are some aspects of the mentioned romance types I have noticed that were not mentioned
Enemies to lovers:
This often involves them starting to respect each other and trying to understand their foe.
Friends to lovers:
One problem for the couple is if they grew up together, that they might see each other as like a sibling.
Forbidden Love:
How many relationships start these days not despite family being against a relationship, but because of it?
Maybe a plot where the MC starts such a relationship as a form of rebellion against their parent, but the other person cares for them and help them overcome their problems, developing their relationship that way?
Fake relationships
Sure it may be fake to start with, but it's key to point out that the couple know it, and accept it. They know they will have problems with each other, and have to try to resolve things and get along. In a way they can be more honest with each other than normal couples as they don't have to worry about ruining their relationship.
Opposites attract:
Pretty well covered. However, there must be a reason for them to be around each other to start with. If there is not, then it can feel forced.
Second chance relationship:
They may have to deal with what caused the separation in the first place. If it was because they wanted to follow different paths? It can be easily dealt with. If it was because someone broke them up by making to seem like they cheated on each other? Then you have to expose them.
There is also the issue of people who knew them if it was not a happy split.
Arranged marriage:
Don't follow them, so I can't say much, except if they are different backgrounds there may be a nice clash there to deal with.
I do like the idea of an arrange marriage where both parties don't want it, and once married to bring the families together skip out, leaving both families wondering WTF will happen.
Memory loss:
Should mention that the person who lost their memory would want to learn more about their past and be told by their partner who might not know everything, or lie to them to create the relationship, like in the movie Overboard.
I am not big on romance as main plots, but can appreciate it as a subplot