nicorac I had this exact same issue.
I went back through and followed the instructions to the letter.
The key difference was following the parts on "Domain Machine Preparation" and "Join the Linux Host machine to your AD domain".
In particular I had to add a reverse DNS zone, setup a PTR record with FQDN of the linux sql host and before joining the realm, ensuring that the hostname of the linux server had the FQDN.
I haven't determined which of the steps was the key missing piece, but following and verifying all of the steps moved past this issue.
I'm not 100% done yet though. I'm now stuck on creating the keytab and getting an error about No credentials found for supported encryption types. Working through that one at the moment.