xpra: insufficient permissions to use socket path '/var/run/xpra/tux-5'

On the remote host, you have to be added to xpra group, e.g:

sudo gpasswd -a user_name xpra

xpra: USE flags to install on gentoo without using nvidia

/etc/portage/package.use/xpra should be:

x11-wm/xpra -video_cards_nvidia
x11-base/xorg-server xvfb

xpra on gentoo: cuda is required

/etc/portage/package.use/xpra:
x11-wm/xpra -video_cards_nvidia

xpra: More responsive remote connections

Add abbr to fish:

abbr cxpra "xpra seamless ssh://server 'terminator' --ssh=\"ssh -o Compression=no -o TCPKeepAlive=yes -o ControlMaster=auto -o ControlPersist=600\" --speed=100 --encoding=rgb --no-notifications --no-bell --speaker=no --microphone=no --dpi=96"
--min-speed — higher is faster. 100 is the maximum, meaning "always encode as fast as possible, never slow down for quality."

--min-quality — lower is faster. 30 means "allow aggressive quality reduction to save bandwidth." Setting it to 0 lets xpra reduce quality even further dynamically

Or run persistent server on the remote server

On the server: xpra start :100 --start-child=xfce4-terminal
On the client:
xpra attach ssh://server/:100 --encoding=jpeg --min-speed=100 --min-quality=0 --compress=1 --bandwidth-detection=yes --pixel-depth=16 --auto-refresh-delay=0 --video-scaling=2 --dpi=96