Ask HN: Anyone Using External Drive for iCloud?

I've read about some people using symlinks for iCloud to point to an external drive, but am not sure how reliable this approach is, and can't really get a straight answer from ChatGPT.

I have some files on an external drive which would consume my remaining storage capacity on the internal drive, and wish to sync them with iCloud.

The data is for a private dataset that I've built for machine learning purposes and is roughly 400 GB.