I updated yesterday - now it’s much slower ...
Hard reboot your phone (depending on which model -hold at the same time either the home button and power button until it completely shuts off - then power back on, or iPhone 7 and beyond: Press the power button and the down volume button until it shuts off, then turn it back on). Fixes nearly every one of the “slowed my iPhone down” issues.
All bets are off if your internal storage space is nearly full...