3D Viewport Scaling changes out of my control

Hello,
I ve got an issue about Viewport Scaling. When I navigate around a model to look at it by diffrent angles, my viewport resolution changes dynamically. I've changed Viewport Sclaing from ''Auto'' to ''None'' but didn't work at all. Do I miss something? Or is it lack of hardware or driver?
PC:
CPU: AMD R9 5900x
GPU: AMD 6700XT Sapphire Nitro+

RAM: 64 GB 3000 Mhz CL16 Crucial Ballistix
MB: Asus Rog Strix B550-F Gaming Wifi
OS: Windows 10 Pro (Retail Key)