I know it's annoying and probably feels like a backwards step, but you should try and accept it, a majority of the time you won't notice a "huge" difference. other than that the S21/S21+ are still great phones. give it a few days and see how you feel about it. I rarely use it myself, I've been using Adaptive 120hz FHD+ on my S21 Ultra for around 80% of the week I've had it. mainly because I only came from S20 Ultra and had 60hz FHD+ set on that constantly, but also because I don't notice a huge difference. Of course it's completely your choice, but don't let that one thing ruin it for you.