If this was my situation I'd try the following.
I use the Netflix App on my Samsung N20 Ultra 256Gb 5G phone and haven't experienced this issue although bear in mind we all set up our phone's differently and have different apps etc.
Which software update are you on ?
Perhaps send feedback via your Samsung Members App along with any app crashes logs so they can also look into this.
I wish you all the best with this.
Current Phone >Samsung Z Fold³ 5G.
Previous Phone > Note 20 Ultra 5G SM-N9860.
are you sure s21 is superior? just go the page designated for teh S21 series, it has just as many problems as the s20 lol