I've been in the thermal suites for MSC Seaside, Meraviglia, and Seascape. Seascape was most recently (Jan 2023).
Here were my notes:
Thermal suite is very similar to those on Seaside and Meraviglia. I would give the nod to Meraviglia as it has more comfortable loungers in the relaxation area and in the salt room. Seascape has snow room, bright light and dark sensory wet saunas, soft sauna and Finnish dry saunas, 3 heated tile loungers, cold showers (2 lemon, 1 mint, and 2 pine scents), warm shower (2 orange scent), one walkthrough cold to warm shower, and a thalassotherapy pool.
From the videos I've seen so far for Sun's Enclave it looks like there are more heated tile loungers (eight), but the salt room has bench style seating as opposed to loungers like MSC has. Both have a thalassotherapy pool, dry sauna, and sensory showers. I only saw one wet sauna in the Sun video. Don't think I saw a snow room.