This article explains the SRM license key impact during an upgrade from SRM 8.X to VLSR 9.0
VMware Site Recovery Manager 8.X
VMware Live Site Recovery [VLSR] 9.0
Site Recovery Manager preserves the license only during an upgrade within the same version, for example: from version Site Recovery Manager 8.8.0 to Site Recovery Manager 8.8.0.3.
During an upgrade to a different version, for example: Site Recovery Manager 8.8.0.3 to Live Site Recovery 9.0.2.x, Site Recovery Manager reverts to an evaluation license. After the upgrade to Live Site Recovery 9.0, you must reinstall your Site Recovery Manager 8.x license key.
When upgrading SRM from version 8.x to Live Site Recovery 9.0, there is no need to upgrade the license key. The existing Site Recovery Manager 8.x license key will work with VLSR 9.0 version and does not require an upgrade, but it needs to be reinstalled after the upgrade to version VLSR 9.0.
if the license shows as expired after upgrading to VLSR 9.0 version assign the license as below
vSphere Client UI -> Hamburger Menu -> Administration --> Licenses --> Assets --> Solutions --> Select the VLSR asset --> Assign License --> Select the correct SRM 8.x license and click OK