The documentation you shared is for version 8.10, not 8.1.
In the Elastic documentation site you can change on the left side to look at the documentation for a specific version, if you change it between version 8 minor releases you will see that the page only exists from version 8.5
Since you are on version 7.16, you would need to upgrade to version 7.17 and then you could upgrade to version 8.10.
I have few other doubts: I see that the documentation examples of TSDS use a policy that enables searchable snapshoots, are they required to reach the mentioned 70% compression ? Are they necessary for using TSDS?
OK, in the documentation it is not mentioned that searchable snapshoots are required, on the other side I see having the policies does not require to have a searchable snapshoot phase but would be logical to have it.
Also I never have used them, I'll go for the version update.