Just an observation…I visit several parishes within my area, and find that the parishes with the " old style confessional boxes" almost always have a line of penitents waiting to go to confession and the more modern reconciliation rooms don’t.
In my experience, Confessions lines are most linked to its convenient availability and the attitude of the pastor.
The Cathedral downtown, with traditional confessionals, always has a line during its lunchtime confessions. I’ve never been there at other confession times, so I don’t know.
Another parish has confessions before every Sunday Mass. They have Masses every hour on the hour in the tiny church and the confessionals are inside the church, so Confessions are happening while Mass is going on. Always a line.
Another nearby suburban parish built in the 80s (ugly, with Reconciliation rooms - but always an option for a screen) has a fantastic priest who really values the Sacrament and preaches on it. Confession lines are long. Really long.
Another local parish always has lines, often 10-15 deep for each of 3 priests. They offer confession three times each week and have something in-between a confessional and reconciliation room. (No cozy seating and soft lighting, but it is a room, with a screen and kneeler that you can walk around to reach a chair.)
My own parish always has 3 or 4 people in line, with no confessional and no reconciliation room. Just an icon of Jesus. That’s not a long line, but we are a parish of 20 families, so not bad. We offer confession for 30 minutes before every service, which for most people means Sunday morning. My pastor preaches regularly on the need for confession.
The FSSP parish, with its confessionals and multiple scheduled time each week, plus the emphasis of the priests on the sacrament always has lines.
Another parish that I’ve tried to go to, but never succeeded, has traditional confessionals. They offer confession for 30 minutes each week, purportedly. I’ve tried three times, and the church has been locked up tight, with nobody else around each time.
Just anecdotal, of course, but I personally have not noticed a correlation between the style of confessional and the number of people approaching the sacrament.