Hey, I will be really glad to know some details.
Can you please provide some info about where did you test it? Thanks in advance.
Because a few people asked me for nextjs demo, so I have created a small one and it's showing 100 Performance on the lighthouse. https://ninja-keys-demo.vercel.app/
Also, it's using backdrop filter for blur effect, that maybe slow, but it's easy to change in css variables