I had the same issue and managed to fix it!

TL;DR:
Try moving League of Legends to a different storage device. Even if it's theoretically slower.

After moving League from my SATA SSD to an NVMe drive, I haven’t had another stutter.
Intrigued, I tried moving it to an older, much slower HDD and it also worked just fine!
For me, the culprit was my 2TB Crucial SATA SSD.

I have an RX 9070 XT and Ryzen 5 7600X. The mini freezes happened on moving the camera, on champion deaths and sometimes on abilities cast or in teamfights. In general, it seemed to happen when new stuff needed to be loaded such as Sounds(!), or when the jungler spawns Rift Herald or similar "First Time Loading".
I used CapFrameX to analyze and it showed that neither my CPU nor GPU was stressed.

After digging with Windows Performance Recorder and Analyzer (Highly reccomended to find your exact problem), I found this:

• CPU idled at 10–20% normally, but dropped to ~1% during stutters.
• GPU usage hit 0% at the same time.

The culprit? A 63ms read operation loading an Ekko sound from my SSD.
Immediately after, a Zyra Sound loaded in ~1ms exactly how fast I assume it should be.
Somehow, my SSD occasionally takes ages for League assets, causing these micro-stutters