Oh dear. This was my parents too...and then Mom started her decline into dementia...and Dad is still letting her call the shots. Even though they are not rational and coming from a place of dementia.
I am sick about it and don't know what the answer is. But like the PPs above, I try to get my dad 1:1 when possible. He admits he feels trapped but still doesn't want to contradict her. Ever.

Is he unhappy? Or is it that you would be unhappy if you were in his situation?

There is a similar dynamic between my parents, and my crazy mother has been able to persuade my father to do really mean things, which I don't think he would otherwise have done.

However that is only part of the story for my parents. He is in charge of the purse-strings. Thank goodness, my mother knows nothing about money.

Take him on a vacation - just him. Short of that, take him out to dinner, just him. Go for a walk. Insist on a relationship with him - just him. You have some power here ~

You cannot dictate the dynamics of anyone else's relationship.

I saw this happen with my DH's grands. The old man died first and then grandma went nuts with alzheimers/dementia. Seems they kinda needed each other.

My guess is something has gone on in the relationship that you are not privy to.

I second the suggestion to find 1:1 with your dad.

Can you see him alone, without your mother? You can't change their dynamic, and neither of them probably want that, but that way you could talk to your dad one on one sometimes.

I've noticed over the past year that my parents, both in their early 70s, have settled into this dynamic where my mother pretty much dominates everything to the point where it's starting to seem like my father is being emotionally abused. My mother pretty much decides everything for him, and whenever I try to gently call them out on it, he just says, "what's good enough for mom is good enough for me," or "she's the boss."

For example, when they were visiting this past weekend, my father started to talk about how he was shopping for a better gardening tool at Home Depot. Now, the man hardly talks at length much anymore, so whenever he does, I let him go on. It's good to see him interested in something. My mother suddenly butts in and tells him not to bore me about such a thing and proceeds to ask the same questions she always asks about my kids and then, moves the subject over to religion, a subject she can never get enough of and which, for me, has become unbelievably dull. When I interjected and told her to let my father finish, he just agreed and said that my mother was right.

I don't know if I should just accept this as it is, that maybe he is strangely happy being lorded over by her at this point in his life. I just know that I was raised to never tolerate anyone treating me that way. I can't believe this is how my mother, who would NEVER accept being bossed around or interrupted, is now doing this to my father. It's even extended to things like family events on his side. I got the sense that he wanted to attend the funeral of a cousin who passed away. Granted he hadn't seen that cousin in ages, but still, he wanted to go. My mother always hated my father's side of the family and based on the conversation, I get the sense she talked him out of it, saying it was too far away. He just let it go from there, saying it's too far. He could've just said he'd go himself but I don't think he'd do anything without her at this point.

Again, I don't know. Maybe this is just what makes him comfortable now? It's just so sad.