@Rune_Andresen-Breivang_VGS : Thanks a lot, your note about using a printer URL in the form of smb://username@printer-address pointed me into the right direction - Sonoma seems to have lost its multi-domain support with SMB printing! I can confirm, that Sonoma 14.1 works at our site now, when users authenticate with username instead of domain\username as they used to do pre-Sonoma. Note, that this works without the username@printer-address hack you proposed (i.e. we simply use smb://printer-address/queuename). But we are just lucky that it works for us, since the print server is only aware of one domain. If you have domain trusts in place you might be out of luck.
Actually, I can't tell if 14.1 did make any difference, it might have worked in 14.0 already, when not using the domain\username form for authentication.
I still consider it a bug though, that Apple is kindly asked to fix.
BTW, this is the error I get in /var/log/cups/error_log (with CUPS debug logging enabled), when using the domain\username form of authentication:
D [30/Oct/2023:09:38:27 +0100] [Job 7] rpc_open_printer: RPC error 0x16c9a011
D [30/Oct/2023:09:38:27 +0100] [Job 7] RpcOpenPrinterEx returned 0xc002001d!
E [30/Oct/2023:09:38:27 +0100] [Job 7] Unable to connect to printer
