It seems NFSv3 didn't really fix the issue and ran into others (e.g., weird user IDs on remapping). I've gone back to NFSv4 and increased the number of NFS servers/processes from the default of 4 up to 5 to see if that helps.
As discussed with reddit user u/ben_theredonit, the pi4 fails to utilize the emulationstation.sh at the time of posting when shutting down. So editing emulationstation.sh, will not work to play a video before shut down. I solved the problem through a roundabout solution. I found a shutdown button that can be added via the carousel, developed by Steve Smith. Below is his video and in his YouTube description, his files:
The user Lampros in the youtube comments has a guide to install, if you find yourself getting the permission denied error, as many people in the comments have, I fixed mine by simply typing "sudo" in front of the "chmod +x" command
From there, I simply changed the 'rom' shutdown script adding the "sudo omxplayer RetroPie/roms/shutdown/shutdown.mp4" code and it worked.
Big thanks to reddit user u/ben_theredonit, who offered their help.
I hope this helps anyone that was lost as I was when trying to add a shutdown video.
@huhogany Hi. where do i even find that line /opt/retropie....etc, etc? I am so lost and confused. Do I look for it on pc or use the pi4 gui screen? i have no idea where to find this. Is it a command line?
UPDATE: I got it to work. What I did...
Updated post fixes in vman 512 image... reboot
set audio output to headphones
Most likely the USB stick is not 'mounted' (therefore inaccessible) when the splashscreen starts, so the video cannot be read and the splashscreen fails. Copying it to /opt/retropi.. will copy the splashscreen on the SD card, which is immediately available on boot.
@kristjan1111 As other services started on boot, the splashscreen has to wait until the system is minimally start before it can start. Since the splashscreen image/videos are on your local disk, there's nothing that can be done before the disk check is complete.
I remember that there was a bug on RPI's related to fake-hwclock that would make the disk check trigger every boot - https://www.raspberrypi.org/forums/viewtopic.php?t=198937&start=25 - so try to run a system update and see if it fixes the long boot time.