APEX snippet to give the current user access to the community (will bring back the `Workspaces | Builder` buttons)

apex-adjust-community-permissions.cls

String endpoint = URL.getSalesforceBaseUrl().toExternalForm()+'/services/data/v47.0/sobjects/NetworkMemberGroup';
HttpRequest httpRequest = new HttpRequest();
httpRequest.setEndpoint(endpoint);
httpRequest.setMethod('POST');
httpRequest.setHeader('Authorization', 'Bearer ' + UserInfo.getSessionID());
httpRequest.setHeader('Content-Type', 'application/json;charset=UTF-8');

// Change network id and profile/permission set Id
httpRequest.setBody('{"NetworkId":"0DBB00000004d57","ParentId":"00eB0000000fegYIAQ"}');
Http http = new Http();
HttpResponse httpResponse = http.send(httpRequest);

may need to adjust the API version in the endpoint URL