I think the issue is a matter of language and lacking a term for making peace with your past.

I feel that "forgiving" someone is accepting whatever happened and making amends in a way that allows a continued connection or relationship as it was.
Whatever caused the trauma was likely bad enough to hurt you and change the course of your life, handing you a mess to sort through for years or a full lifetime.
It can be some pretty horrific things that happen to someone that forgiveness should not encompass.

Holding on to anger and revisiting what happened in one's mind can take forms of either internalizing it and blaming oneself for what happened or externalizing it and blaming the other people. It can be easy for some to "forgive" in some sense of the word when they are internalizing it and laying blame on themselves.

I feel that it is better described as "letting go" or simply "accepting" as a better terminology.

When I was a kid, my dad taught me how to swim in a river. This was a prerequisite for being able to go river fishing so he was sure it was safe if something happened while we were in the boat.

Navigating a slow moving river is similar to a swimming pool. The current has little impact on you. A fast moving river will sweep you downstream quickly. Simply being in the current and moving away from a familiar location or the boat you had been in can induce panic.

The first rule is to swim towards the bank but do not get fixated on the point across from you. The current will carrying you along the river and your goal is to go to the bank at whatever point you reach it.

The second rule is not to grab onto anything. In a state of panic and being rushed along the river, a limb sticking out of the water can look like an offer of safety. Grabbing and holding onto the limb will cause the current to pull someone under the water. In a state of panic, letting go of some solid thing seen as safety can drown a person. Realizing the danger, after being yanked under by the current and tossed around in murky waters, one can let go of the limb before you are drowned and continue their journey to the bank.

That anger and those thoughts of the past experience is like that limb sticking out of the water. Holding on will only drown someone faster. The limb that had been grabbed onto does not need forgiveness. It needs to be recognized for the experience that it was and that danger avoided in the future.

My mother provided terrible support through my depression and probably unknowingly framed problems as being with me and not other people. Later in life she made other bad decisions and stepped away again when I had issues with a relationship, preferring not to hear anything about my side of it.

I still have a relationship with my mother, but I haven't "forgiven" those things nor have I dwelled on them and hold anger about them. My mother later started to try to push for repair to the relationship she didn't want to be involved in hearing from me about. I made it clear that was not an area that was open for discussion. I recognized the danger of the limb and didn't grab it.