"quiet" kernel parameter seems to enable skipping the disk check: With "quiet" on the kernel command line, one of the few lines to appear on the screen is "disk check skipped", and the boot completes noticeably faster. (35s instead of 55s, booting from an ISO file on a hard disk)
Ubuntu 20.04.2 behaves the same way.
"quiet" kernel parameter seems to enable skipping the disk check: With "quiet" on the kernel command line, one of the few lines to appear on the screen is "disk check skipped", and the boot completes noticeably faster. (35s instead of 55s, booting from an ISO file on a hard disk)