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"Can a Core i9 machine be a workstation?"

If the term "workstation" has any meaning, then no. A machine that can provide only a few cores, almost no cache, and 64 GiB of non-ECC DRAM is just an ordinary PC, at best.

"If you think not, Lenovo also has tiny Xeons"

Yeah that's not helping any. Intel aren't making competitive products these days. If you want a quiet small form factor machine, you want something like a Raspberry Pi 4 or if you insist on x86 you're going to be looking at specialty low-power parts (see FitPC for examples). If you want something beefier than that, an AMD 5600X on a mini-ITX board, which can be fanless if you're not picky about it fitting into a litre. That can be a very usable general-purpose desktop but it's not a workstation. If you want something powerful, it's going to have some kind of AMD SP3/sTRX4/sWRX8 in it and it's not going to be small, though there is a mini-ITX board on the market that can still handle 256 GiB of DRAM albeit at greatly reduced performance. These days my minimum threshold for "workstation" is 16 cores, 64 MiB of cache, 256 GiB of ECC DDR4, and 3x 4K60 DisplayPorts. You're not going to get that from anything in this line. Also, "workstations" don't have SATA, a protocol that was obsolete 15 years ago and is embarrassingly inadequate for today's solid-state storage. Why would I give up >90% of my storage performance by slapping an ancient front-end on it? Workstations are built for performance; these days performance means PCIe gen-4 NVMe, exclusively. SAS is acceptable for rotating media in data centre based cold storage arrays. SATA has no place anywhere but the bottom of entry-level, and then only for rotating media.

At least until Sapphire Rapids is available, Intel aren't even worth looking at. If you're building machines around Intel processors, I won't be your customer regardless of form factor. I'd have said the same about AMD prior to Zen. If you're an OEM you need to be flexible and build with the current leader, not whoever gives you the biggest rebates out of a marketing slush fund.