I already had a seperate disk added to a cluster as a resource but when I tried to change logs under default database locations, the disk wasn’t listed. setting the path to use the disk anyways and trying to create a database revieled the anwser.

You need to make add the disk resource as a dependency to the SQL Server resource in Cluster Administrator. Notably, you can’t do this while the cluster is online, which is pretty stupid. Hit take offline, add it, bring it back online, and then you’ll see the additional drive letter in the server properties in SQL Management Studio when trying to change the default paths for databases or logs.