I have tried same with the latest version 2.466 and Seems same issue.
Thanks for checking. Yes, I've confirmed that it behaves this way for 2.458, 2.464, and 2.466. I was wondering if you had been using a version where it behaved differently than is reported in this bug report.
I checked Jenkins 2.414.3 using Java 17 with the most recent plugin releases supported on Jenkins 2.414.3 and confirmed that it behaves the same on Jenkins 2.414.3 as it does on Jenkins 2.466. That makes me think that it is probably a bug in the plugin that is causing the issue, not a bug in Jenkins core. You'll need to use the workaround of creating the secret text as a separate step after saving the SonarQube definition.
Thanks for reporting the issue. I can duplicate the problem with the following steps:
The workaround is to save the definition of the SonarQube server by pressing "Save" without adding the credential, then add the credential from the same button in a second step.
The same problem is visible in Jenkins 2.458. As far as I can tell, this is not specific to any recent change in Jenkins core.