yeah i always do this with tigervnc server on X11. create a vncpasswd file and place xinitrc on ~/.vnc/xstartup, then run vncserver :1 to create X11 display :1 and vnc server on port 5901. if you want to start vnc on a (physical) session already running, you can run x0vncserver. there's also x11vnc but x0vncserver feels much faster for me.
yeah so i was thinking the 'android desktop mode' you meant was the linux virtualization thing lol. termux-x11 is different from that, no virtualization, just a normal android app so in fullscreen mode can work like a linux x11 session with access to android files, but can just click home button to run android stuff.
if you can connect it to a large display, you can just use termux-x11 and use it like any other unix/x11 desktop machine. i do this with a samsung tablet.
i think you can just use
yt-dlp -x {youtube link}to get audio btw.