Moderator: Please post threads into the best product area. Thread moved to the ESXi area.
You will need to provide more information before others can help you - such as the disk configuration of the ESXi VM, screenshots of your datastore view and of your storage device view from within the vSphere Client.
Ignore the error message. This is simply a GUI bug, and occurs because of the missing datastores.
Regarding the datastore. ESXi 7.0 - by default - consumes up to ~130GB on the installation disk. In order for ESXi to create an additional VMFS datastore on the installation disk, you need to configure a larger disk. In case of a virtual lab, I'd suggest that you simply create two virtual disks, one for the installation, and one on which you will create the datastore. For details see ESXi 7.0 Hardware Requirements
For lab purposes, you can alternatively specify/reduce the size for the OSDATA partition size by appending e.g. autoPartitionOSDataSize=24576 to the installer's boot options. Please read https://www.virtuallyghetto.com/2020/05/changing-the-default-size-of-the-esx-osdata-volume-in-esxi-7-0.html for more information about this.