The Lounge category is no longer included with new installations, but you could certainly recreate the concept, and adjust your site’s TL3 thresholds so that it’s easier to achieve and/or retain.
Just filter settings for “TL3” to see all the options. TL3 promotion min duration is probably the key here – set it to 10,000 days or something.
Edit: note that TL3 includes a bunch of advanced permissions for using the site – not just category access:
Trust Level Permissions Reference - Documentation / Using Discourse - Discourse Meta