UXP command line installation support is coming with Creative Cloud Desktop app version 5.7 in April, for both .CCX and .XDX files. I’ve put all the details in this blog post: How to Install UXP Plugins Using Command Line Tools | by Erin Finnegan | Adobe Tech Blog | Mar, 2022 | Medium (this link avoids medium.com’s paywall).
Please not that the rollout of CCD is not instantaneous for all users, it rolls out incrementally between March 31st and April 8th.
If I’ve gotten something wrong in the article, do let me know!
If you’ve got questions, ask them here.