Yes. But what are you trying to do? Usually those requests mean someone's trying to brute-force existing addresses, which won't work.
I don't want to search for specific patterns like 1Love, but create many addresses and pick out the best patterns that I might like.
That's going to be a lot of work. You can't humanly read millions of addresses, and vanitygen creates that in seconds.
In the past, I've brute-forced mini-private-keys, and ended up with about a gigabyte of data. I could search for keywords, but even millions of addresses are barely enough to find something nice.
Suggestion: create a list of possible keywords, and use that as input for vanitygen. That way, it can search for thousands of different prefixes at once, and you may hit something good.
Does VanitySearch also support 12 or 24 seeds?
No.
is there possibly a possibility to convert a private key afterwards to a seed?
No.
I think I read something that you convert it into bites and then the bites into words.
Well, yes. But that will just be another way to write down your private key, it won't give you a seed phrase that a standard wallet can use to derive your vanity address.