Would a third cat help my cat leave my other cat alone?

I found a kitten back in 2015 when I was teenager. I went to college a few years later and found another kitten.

2015 kitten had been raised with a very docile dog and never met a cat before.

2020 kitten was raised with cats and had one particular cat he would play rough with. They were really close and loved each other.

I introduced the cats back in 2020. Older cat hated the new kitten. 2020 kitten stayed away. When 2020 kitten started getting older he wanted to play with the older cat, but she wanted no part of him.

Obviously the year is now 2026. My cats are now 10 and 5, almost 11 and 6. She still hates him. He wants to play. He jumps on her. He chases her. He loves to sneak up on her. He used to get a little aggressive when he played, but he doesn’t do that anymore.

I’ve been wondering if maybe another cat would help him? Maybe he’d finally have someone to play with besides me. There is the chance that the cat also doesn’t want to play and there’s a chance they could gang up on my older cat too and she’ll be miserable.

Any advice on how I can help ease the tension between them? Would another cat help or is there something else I need to do?

I’ve tried everything. Calming pheromones. Toys. Stimulation. I’m out of options.