"So if I want the disk to be thick, I have to change this% so it sets aside disk space."
So create a new Storage Policy and add rule for OSR=100 and apply this to the VM/vmdk Object(s) - don't do this at the VM disk primitive level (e.g. setting disk type to Thick Eager-Zeroed) as these over-ride Storage Policies and you won't be able to change that disk to 'Thin' (OSR=0) using Storage Policies should you want to in the future.
"However, I did a test and the result was different from what I understood."
Looks completely normal to me - Thick disk is using 2GB (2x1GB as it is FTT=1) + small amount of vSAN overhead space, Thin disk is using whatever it is using x2 + vSAN overhead space.
Don't do it this way though - use SPBM.
I read that the default policy defines the disk as thin, because the (objetc space reservation) option is set to 0% by default.
So if I want the disk to be thick, I have to change this% so it sets aside
Yes, adding a rule with OSR=100 to the applied Storage Policy is essentially a way of reserving the space as you would Thick disks.
In general making a new SP is advised, e.g. create/clone from default then modify as needed, then apply it to the Objects/VMs.
"So if I want the disk to be thick, I have to change this% so it sets aside"
Yes, It's not Thick like EZT Thick, but it is reserved.
Why do you have seemingly random URLs in your comment?