How can I remove LGBTQ+ themed wallpapers that is included in iOS 18.4.1?

You don't, but you also don't have to use them. There are many things you cannot delete, including emojis that you may not like or don't want to use. In both cases, you have the choice to use anyone you want.

You can’t, but you don’t have to use them.

You simply cannot remove anything built into iOS. You aren't required to use any wallpaper you don't want to use, so don't use them.

🏳️‍🌈🏳️‍🌈

it is simply built into the software. You cannot remove it. You just shouldn’t use them

You cannot remove them but you can choose not to use them. If you don't use them you'll never see them, so if you don't want to see them, that is your solution