I’ve had good experiences with Rustdesk. The client is open-source and the no-cost server components (ID and Relay servers) are self-hostable. The remote server works on X11 and Windows. I use this script to run XFCE+Rustdesk in a headless session:

export SERVERNUM=69
export SCREEN_SIZE='-screen 0 2560x1440x24'
export DISPLAY=":${SERVERNUM}"
export XDG_SESSION_TYPE=x11

xvfb-run --server-num="${SERVERNUM}" --server-args "${SCREEN_SIZE}" startxfce4 & disown
sleep 1
flatpak run com.rustdesk.RustDesk & disown

Sunshine + Moonlight is also a good choice. I have Sunshine installed on a box at home and use Tailscale to connect to it from the Moonlight client. At 1440p 60 FPS it has no visible compression artifacts and responsive enough for gaming.