just to add to @Fiona26 's post whilst phone calls get through fine fine power Saving Mode does lower performance and prevents background sync. It will also limit GPS, not something to be on constantly really though there will be times when there is a need to save Battery. Details on the mode in this article ttps://www.samsung.com/uk/support/mobile-devices/what-is-power-saving-mode-on-my-galaxy-phone/
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.
My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 5.0,Android 13 .