Book two of the Rise of the Arcane Aristocrat series.
You can find book 1
And book 3

I was the Rift Magus—master of space and time, protector of worlds. For decades, I defended my realm with unmatched power. But when I was reborn in the body of Lucian, a young noble in a different world, I had to start again.

My strength was diminished but my knowledge remained, and I quickly reclaimed fragments of my lost powers--and even found some that were new.

But this new life came with intrigues and rivalries of noble Houses, and obligations as well--one of which threatens to escalate out of control and put my progression at risk.

If I was the young noble I seemed to be, I would be out of my depth.

But I am not Lucian. I am the Rift Magus, and I've dealt with my share of both family obligations and unspeakable horrors, growing stronger all the while.

I can do it again.

I will do it again.

There's nothing in this world that can stop me.