> large object promisors will work like this: - You push a large file to your Git host. - In the background, your Git host offloads that large file to a large object promisor. - When you clone, the Git host tells your Git client about the promisor. - Your client will clone from the Git host, and automagically nab large files from the promisor remote.

This doesn’t seem to solve the issue of the long download time / big repo size. Or is the author describing the use of promisors remotes in conjunction with partial cloning? Unless I missed something it is not stated explicitly.

Yes, in conjunction with shallow and/or partial cloning. The clone --filter is for shallow cloning