This is not possible with the WP_Query. You can specify relationship inside the tax query and inside the meta query, but, you can’t have the query where meta and tax query are connected by OR.
You can always build the SQL query the way you want it, not relying on the WP_Query at all to filter posts exactly the way you want it. Or, you can use two WP_Query objects, one with meta_query, other with tax_query, and merge the results. In case you have a lot of posts, or you need pagination, that will be a challenge to make optimized.