How to speed your iPhone up
Easy, back it up, reset it, restore it, and update it.
That’s all I did, and I wasn’t trying to speed it up. I thought I had a working iPhone 8, well other then the beat up screen. Don’t use such a phone without a screen protector, it’s rough, not pleasant to use your finger on it.
Did I reset it? I did log out of my Apple account. I probably reset it. I’ll find out, if somebody hacks into my stuff.
There’s a nice guy selling a Motile laptop, without doing a secure erase, he’ll reinstall Windows if you want. Use some file recovery software, and their data will be recovered. Somebody did that to me once, I was stupid and didn’t shred the drive. There won’t be a next time, but if there is, no drive will be included.