I don't think the meta version of Permissions-Policy ever got implemented. "http-equiv" isn't a magic "here's a HTTP header I forgot to mention" pixie dust.
Better stick to the actual recommendation of adding the header in the server configuration.
Whilst http-equiv is said to be an enumerated value, so far as I know in Chrome, it actually is "magic HTTP Header pixie dust": [0]
And whilst in Firefox parsing of the element is more spread out, they accept a very wide number of headers that aren't documented, and you'll find examples on MDN for any number of headers using http-equiv which aren't specified in the standard or on their docs for http-equiv itself [2] (For example, X-DNS-Prefetch-Control [1]).
Better stick to the actual recommendation of adding the header in the server configuration.