Hey there, Shivalt!
Thanks so much for using Apple Support Communities.
Being able to use your iPhone without any frustrating lag is definitely important. Let's see if we can figure out what might be causing this.
To start, you mentioned that you're running iOS 14 but are you fully up to date on iOS 14.5.1? If not, here's how you can update: Update your iPhone, iPad, or iPod touch
Once you're up to date, test the device for around 24 hours and see if you notice an improvement. It can take some time after updating for the phone to get back to the best performance possible which is why we recommending testing for some time.
If you are already up to date, however, then we'd recommend focusing on your storage and making sure that you have plenty of space. If your device is low on storage, it may explain the slow performance. Here is a link with more info: How to check the storage on your iPhone, iPad, and iPod touch
Good luck!