Well, on one hand, it’s true, the Catholic Mass is not a time for socialization and whatnot. On the other hand, however, if people happen to make eye contact at whatever point, it is rude to not return a smile or at least acknowledge that a person made eye contact with you if you notice it.
For a Protestant or non-Christian who has never been to a Mass, this could potentially be jarring to come to what one may consider a “social gathering” and then not be enthusiastically greeted or whatever; for this reason, I think it’s good to have near the entrance a table/rack with information on it that would be accessible/noticeable to newcomers, whether Christian or non-Christian.
Otherwise, the best way to meet people at a Catholic parish is, not just going to Mass, but also going to parish activities. Unfortunately, many parishes do not have the family-type atmosphere that they should, and may not have very many parish activities. However, for someone like you who is coming back to the Church and may have the experience with a close-knit Protestant community (did you?), it will be worth it to search for an active parish community so that you can have the support and fellowship you need.
Although obviously feeling welcome is important and can be a factor in one’s conversion/reversion, one of the beautiful things about the Catholic Church that I hope all people can recognize at some point in their life is that, even when one does NOT feel welcome by the people inside the Church, there is Jesus Christ Himself present in every tabernacle around the world, waiting for all human beings to come to Him, and nothing about how any parish member treats newcomers will change that!
Welcome home - God will certainly bless you for coming back to the Church if you do your best to live a holy life!