@protivakid based on what you told me about inserting the SD card, I then knew that
DEVO_CONFIG->device_signature = st.st_dev;
has to be the problem. then I saw in usbloader gx code that cyan (way back in 2012) changed that line to
// st.st_dev doesn't work with our current device type. It returns Wii_UMS 'WUMS' instead of Wii_USB 'WUSB'.
// Only last two letters are returned by DevkitPro, so we set them manually to Devolution config.
DEVO_CONFIG->device_signature = st.st_dev == 'SD' ? 'SD' : 'SB';
at some point in time st.st_dev became broken maybe by a change in libogc or devkitppc. I can't seem to track it down or find where
@Cyan got his info from. anyway I'm assuming that older version of wiiflow that it worked was compiled before st.st_dev was broken and afterward nobody caught it because they switched to nintendont or they always had a sd card inserted like me.
I added that change in wiiflow lite and would love for you to try this download -
https://www.mediafire.com/file/m7wu278cgjn5ir4/wf5.4.7devo_test1.zip/file
It works for me but I have an SD card and sorry don't feel like trying to move everything to USB to test it.
edit: i just found where cyan and tueidj talked about it here -
https://gbatemp.net/threads/devolution-public-release.330554/page-54#post-4339227
it appears because wiiflow and usbloader gx use custom usb2 interface with a non-standard device id.
The proper device ID for the SD slot is defined here -
https://github.com/devkitPro/libogc/blob/master/gc/sdcard/wiisd_io.h
and for USB here -
https://github.com/devkitPro/libogc/blob/master/gc/ogc/usbstorage.h
edit#2: so I think i now know why Fix94 added devo mount and unmount. wiiflow has 2 sd interfaces and 2 usb storage interfaces. for each - one is a custom and the other is modified code taken from libogc. when nount devo is called it uses the modified libogc code which will actually provide st_dev with the proper device ID as tueidj stated.
but at the same time so does cyan's fix.
so by me removing mount devo I probably broke it for USB users without a SD card. but this new fix by cyan should restore it.