Is it necessary to clean the memory on your iPhone

Then try to free up iPhone device storage see this Apple articles below:

If you need more space for an update on your iPhone, iPad, or iPod touch

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

How to check the storage on your iPhone, iPad and iPod touch

How to check the storage on your iPhone, iPad and iPod touch – Apple Support (UK)

Clear Other storage on your iPhone or iPad

Clear Other storage on your iPhone or iPad - Apple Support

👉 What's the difference between device storage and iCloud storage?

What's the difference between device storage and iCloud storage? - Apple Support

where do you see the 'notice'? is it a popup when browsing the internet?

I don't think 'cleaning' memory is something iOS would tell you to do.

It's likely something that will steer you to the App Store and want you do download an app that has false claims

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support