Can I install iOS 13 for iPhone 6

you cannot. The iPhone 6 does not have enough RAM to run iOS13.

Can’t install ISO 13 on iPhone 6

That is correct. And you have already had an answer to your post and it has also been posted here by muguy, your iPhone 6 does not have sufficient RAM to run iOS 13 or later and you cannot add it to your iPhone. No matter how many more times you post the answer will always be the same.