NVENC Support - flathub/com.obsproject.Studio GitHub Wiki
This package does support NVENC but you must first have CUDA properly configured on the host. This is distro dependent but here is how to do it on some distros:
Fedora
RPMFusion
# dnf install xorg-x11-drv-nvidia-cuda
# systemctl reboot
Negativo
# dnf install nvidia-driver-cuda
# systemctl reboot
Archlinux
https://wiki.archlinux.org/title/NVIDIA#Hardware_accelerated_video_encoding_with_NVENC