Best approach for backing up data on an iPhone

One of my devices (iPhone 8) was purchased from a third party.

The device is now faulty but covered under the seller's warranty.

Before sending the device to them, I have been instructed to completely erase the phone, all content and settings.

I have non-backed up photos (I know, I need to sort that), apps with forgotten passwords that are logged in permanently, that sort of thing.

My question is, what is the most comprehensive method of backing up my phone?

Is there any form of backup that will restore every single bit of data to the phone after its been erased, repaired and returned to me?

I am thinking of doing a local backup to my Windows PC using iTunes but I am not sure if this kind of backup would store apps AND their individual data such as login information, all photos including those saved from messaging apps, etc.

What method of backing up will provide the most hassle-free experience as I erase and restore my device to as is now?

Note: I do not have any iCloud subscriptions for storage etc., but I am not ruling it out.