If WF is working fine, you can ignore this issue.
Besides, here is blog about how to change Workflow Manager Certificates for your reference:
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The get-wffarm output is showing a different thumbprint for the OutboundCertificate as the get-wfoutboundcertificate command.
I dont see any problems due to that but I'm wondering how this could happen?
Is it something which we need to get fixed?
Output of get-wffarm (in fact the certificate with this thumbprint is expired):
Output of get-wfoutboundcertificate:
If WF is working fine, you can ignore this issue.
Besides, here is blog about how to change Workflow Manager Certificates for your reference: