Boot messages with 2 empty CDROMs. Debian Bullseye. Kernel 5.6.14-rt7 Everything seems to work. I guess it can be ignored but something must be,.. not right. Same messages for /dev/sr1.

The messages doesn't appear on every boot. Sometimes it boot with messages about /dev/sr0 only. Not sure but i think there were no such messages with kernel 5.6.10-rt5. No such messages with the earlier rt patched kernels,

drivesJun 1 14:02:17 debian kernel: [ 5.953679] 020: Buffer I/O error on dev sr0, logical block 2097136, async page read
Jun 1 14:02:17 debian kernel: [ 5.953681] 020: Buffer I/O error on dev sr0, logical block 2097137, async page read
Jun 1 14:02:17 debian kernel: [ 5.953683] 020: Buffer I/O error on dev sr0, logical block 2097138, async page read
Jun 1 14:02:17 debian kernel: [ 5.953684] 020: Buffer I/O error on dev sr0, logical block 2097139, async page read
Jun 1 14:02:17 debian kernel: [ 5.953685] 020: Buffer I/O error on dev sr0, logical block 2097140, async page read
Jun 1 14:02:17 debian kernel: [ 5.953686] 020: Buffer I/O error on dev sr0, logical block 2097141, async page read
Jun 1 14:02:17 debian kernel: [ 5.953687] 020: Buffer I/O error on dev sr0, logical block 2097142, async page read
Jun 1 14:02:17 debian kernel: [ 5.953688] 020: Buffer I/O error on dev sr0, logical block 2097143, async page read
Jun 1 14:02:17 debian kernel: [ 5.990598] 020: sr 0:0:0:0: [sr0] tag#1 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE cmd_age=0s
Jun 1 14:02:17 debian kernel: [ 5.990601] 020: sr 0:0:0:0: [sr0] tag#1 Sense Key : Not Ready [current]
Jun 1 14:02:17 debian kernel: [ 5.990602] 020: sr 0:0:0:0: [sr0] tag#1 Add. Sense: Medium not present
Jun 1 14:02:17 debian kernel: [ 5.990604] 020: sr 0:0:0:0: [sr0] tag#1 CDB: Read(10) 28 00 00 00 00 00 00 00 02 00
Jun 1 14:02:17 debian kernel: [ 5.990604] 020: blk_update_request: I/O error, dev sr0, sector 0 op 0x0READ) flags 0x80700 phys_seg 1 prio class 0
Jun 1 14:02:17 debian kernel: [ 6.012612] 020: sr 0:0:0:0: [sr0] tag#2 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE cmd_age=0s
Jun 1 14:02:17 debian kernel: [ 6.012614] 020: sr 0:0:0:0: [sr0] tag#2 Sense Key : Not Ready [current]
Jun 1 14:02:17 debian kernel: [ 6.012616] 020: sr 0:0:0:0: [sr0] tag#2 Add. Sense: Medium not present
Jun 1 14:02:17 debian kernel: [ 6.012617] 020: sr 0:0:0:0: [sr0] tag#2 CDB: Read(10) 28 00 00 00 00 00 00 00 02 00

I'd guess a hardware problem; loose cable, bad contact, broken drive. Even though the drive is empty, the kernel wants to communicate with it (for example, to check if it contains a disk). This fails.

I've seen badly written hardware monitor software complain about DVD drives. Most likely nothing wrong with the drive, it just doesn't return the expected result from a scan.