I can confirm that the Odroid H4 Plus also supports in-band ECC. If I remember right, Memtest86 showed different stats when I ran it with in-band ECC enabled/disabled though I didn't have a good way to test that an error was actually corrected.
Some systems allow forcing an ECC error, but assuming that's not available, if you can adjust memory voltages or timings, you can usually encourage errors that way and confirm memtest detects ECC corrections.
Some systems allow forcing an ECC error, but assuming that's not available, if you can adjust memory voltages or timings, you can usually encourage errors that way and confirm memtest detects ECC corrections.