Lagging phone

These are the basic troubleshooting steps to perform:

A) Check your battery health in Settings>Battery>Battery Health>Maximum capacity... what percentage can you see there?

B) Force restart your iPhone, using these instructions:--> Force restart iPhone – Apple Support

C) if the issue persists, something could have gone wrong during the latest update procedure.

I would try to install a fresh copy of iOS. To do this, create a full backup of your iPhone (1), then restore it to factory settings (you need a computer to perform this step) and, in the end, set it up as new (2).

When done, restore data from your previously made backup (3).

Follow the instructions provided in these support articles:

(1) How to back up your iPhone, iPad, and iPod touch – Apple Support

(2) Restore your iPhone, iPad, or iPod to factory settings – Apple Support

(3) Restore your iPhone, iPad, or iPod touch from a backup

If the issue still persists, contact Apple Support directly using this link:--> Get Support

Regards

Giulio