Did you enter the bios and make sure that
SECURE BOOT and
FAST BOOT are disabled? If you've never been in the BIOS before.......
When computer is off, press the power button to turn it on. Tap the delete key repeatedly, which should get you into the BIOS. Some computers use F2 key instead to enter bios, I don't know what your computer is, so I can't tell you for sure which key is it.
Search the tabs in the bios till you find SECURE BOOT and FAST BOOT and disable them both. Then its usually F10 to save and exit your bios, but might be different in your bios, but you will find it if its different, usually bios provides a key legend at the bottom or the side.
If this does not get you going, then this might be an issue related to several other's on the forum lately who have reported the same issue. In which case, you will have to wait for a resolution, as I have none.
Other then one last thing.....
When you burned the ISO to a USB drive, I assume (though I really shouldn't) you checked the SHA256 checksum HASH for ISO integrity? Actually, I am guessing you hadn't, so you may or may not have a corrupted ISO. Only way to know is to compare the SHA256 checksum HASH and confirm.
Also, I am going to assume (Again I probably shouldn't) that you used Balena Etcher to make the ISO burn, which may have resulted in a bad experience. For windows users, I recommend burning ISO's to USB drives via Rufus or Unetbootin.
I say this, because Balena Etcher is known to screw up drives and not do the burning process properly. But one thing at a time here.