This article will help users to unblock themselves and continue the upgrade.
During an attempt to select 5.1 as target version after sddc manager only upgrade from 4.4.x to 5.0.0.1 selection is blocked with "not interopable: ESX_HOST 8.0.2-22380479 -> SDDC_MANAGER 5.0.0.1-22485660"
The Issue occurs due to a bug in SDDC Manager validations for interoperability because of which 5.1 BOM is validated against 5.0.0.1 SDDC Manager.
To workaround the issue run the below mentioned steps through SDDC Manager UI:
Navigate to "Developer Center" -> API Explorer" -> API Category "Domains" and run "GET /v1/domains" with parameter Type: "MANAGEMENT". In response, search and note the id of the domain - filed like 'id : xxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx'.
Navigate to "Developer Center" -> API Explorer" -> API Category "TargetUpgradeVersion". Execute "PATCH /v1/releases/domains/{domainId}" with domainId from Step 1 and without the body. When executed the request, should return a response: "Status: 200, OK".
This will clean up the previously selected 5.0.0.1 as a target version.