I have the same issue. After purchasing Ylands on 12/9, it worked fine for me for several days, but starting on Thursday, 12/14 it no longer opens. As commanderwarzone describes, launching Ylands from Steam (or directly from it's icon using file explorer) causes the icon to appear on the taskbar and the music to start to play, but the window never opens. My output_log also describes the window size as being 0 x 0.
I have no idea if this is connected, but the problems began after I restarted my computer and had a large Windows X update installed. However, other Steam games still open normally.
output_log.txt
output_log_clean.txt