Is there any incentive to prevent a reviewer from just entering a pseudonym instead of their real name? It would be amusing if after the court order all the company received was "Test User was the one who wrote this review".
Glassdoor would probably be ordered to reveal ip address, and email. To block this the reviewer would need to use a one time anonymous email, and anonymous vpn. In turn, you can’t really trust either of those parties not to reveal your identity (although it might take more time). If I was to do something sensitive on such a site - I would use as many layers of indirection as I thought the companies legal team would be willing to expend in time. After 3-5 such proxies, it’s likely they would give up or at least have to expend 6 months to a year of legal effort to get to your actual identity.
Note that in the above, financial contracts with email providers/etc will be a second method to de-anonymize you, and they are much faster to trace and much harder to avoid.
Your best bet would be to get the free tier of every such service, and use a library computer/public Wi-Fi which does not require authentication and doesn’t have video recordings :shrug: