The partition layout have changed for ESXi 7.0. There is something "new" called OSdata and this will takes all space on your tiny boot drive.
Thank you so much for your quick response! So you think that boot device (SSD in this case) can't be shown in datastore because of "OSdata".
I'm double checking with site owner which you have mentioned, but I've not gotten any feedback yet.
Well, I could use local SSD with vSphere 6.7 and I just downloaded OS ISO images or something like that. I really don't understand why VMware company has changed the structure....