Hello. I'm normally using 74Vfov in games. But in R6 I need more vision. I tried 90 Vfov calculated with %0mm in aimtastic and I didnt notice any precision lost. Is it ruin my muscle memory? Because I want to use 90Vfov only in R6.

You can't "ruin" muscle memory. That's not how it works.

When you perform actions over and over again in a similar fashion your brain, nervous system and muscular structures create "shotcut" pathways that enable you to do the same action at higher speed with the same consistency. It's really rather amazing.

Chaning how you move to do something, will just be using the muscles in a slightly different way than how they have been previously trained. It's like saying "If I wash my car with a left to right wrist action similar to mouse movement, will I ruin my muscle memory for gaming?"

"Of course not"  would be the correct reply.