Like the SaaS apps which are touted as "open source" with small open source clients which are not functional without the closed source backends (or with open source backends which you can't install because of a couple of non-intentionally missing important bits)?

Or like Nvidia's new drivers which are "open source", but all the meaningful parts are either buried in the card or in closed source libraries?

Or like VSCode where the plugins which matter are closed source and it's "open source sibling" VSCodium is banned from using the majority of the plugins?

If the 99.9999% of the tool is open source, but non-functional without that closed bits, can we say the software is open source?

The four freedoms matter, and this is what OSI says, too.