I have just purchased an Acer Aspire TC-885 (Core i5 with 16GB Intel Optane Memory, Intel UHD Graphics 630, Windows 10 Home) and a Lenovo L24q_10 24" monitor (resolution 2560 x 1440). When I first connected it up and turned it on the monitor was just blank and it went into power saving mode (implying that there was no video signal coming from the HDMI socket). There are two HDMI sockets on the PC so I tried swapping the cable around several times and eventually it started working, much to my relief.
The problem is that I can shutdown the PC and it will boot up again ok, but if I turn the mains power off at the socket (as I normally do overnight) then when I turn the PC on I again have the problem of no HDMI video output and the monitor is blank and goes into power saving mode. It came with a sheet of paper saying it has a built-in power management unit that monitors system activity (on keyboard, mouse, hard disk, peripherals and video memory) and if no activity is detected for a period of time the computer will stop some or all of these devices in order to conserve energy. It then talks about Fast Startup, and I followed the instructions to disable it. So it should not be going into any kind of sleep mode as far as I can tell, so why do I need to leave the mains power on all night just so that the video display will work when I power-up the PC the next day?
(It's also very distressing to buy a new PC and find that the video display doesn't work! It should work straight away when you turn the PC on! The first couple of days I wasted 10 - 15 minutes just trying to get the display working.)