As far as I can see, based on the link you have sent it is written:
Endpoint URL:
Endpoints for all business information, attributes, categories, chains and locations search are accessible at https://mybusinessbusinessinformation.googleapis.com/v1/ instead of https://mybusiness.googleapis.com/v4/
The path name for locations endpoints has changed from
accounts/accountId/locations/locationId to locations/locationId
Maybe it was better if you could provide the request uri in the previous version so we could help you more precisely. Anyhow, what I tested in the google playground is as follows:
open [https://developers.google.com/oauthplayground]
after setting your clientId and Authorisation stuff, in the Request URI write
https://mybusinessbusinessinformation.googleapis.com/v1/locations/XXXXX?readMask=storeCode,metadata,profile,serviceArea,labels,adWordsLocationExtensions

instead of XXXXX, write your locationId
you can write different readMask fields, The possible fields for readMask are:
play with different fields to check if you have your desired one or not readMask="storeCode,regularHours,name,languageCode,title,phoneNumbers,categories,storefrontAddress,websiteUri,regularHours,specialHours,serviceArea,labels,adWordsLocationExtensions,latlng,openInfo,metadata,profile,relationshipData,moreHours";
If above does not help you, in the link below I see that all metadata attribute of a location might be:

Click [here] (https://developers.google.com/my-business/reference/businessinformation/rest/v1/accounts.locations#Location.Metadata)