As far as I know you just have to click on the original theme that was on there. It does or should ask you if you want to apply to lock screen wallpaper or home screen. Just like all other android phones.
Yes the default ones look different and it seems there's no way to go back. See this link and it shows what the default ones look like. https://www.google.com/amp/s/www.businessinsider.com/zte-red-magic-5g-review?amp"simple clouds" enables the squares. i can't tell if Default squares looked differetly.
