...Can seed phrase be memorized? It's advisable to memorize seed phrase?
Why don't you try and see if it is possible to remember 12 or 24 words? Of course it is possible, but if you use your brain as storage, then you have to take into account that this storage can be damaged at any time, whether it is due to an accident or some disease that causes memory loss. In addition, keeping such things in your head is not smart for another reason, because someone can use it to find out about them while you are not completely conscious (under the influence of alcohol, drugs).
Why don't you consider uploading it to the cloud?
That is what I did with metamask phrases. I remember the password of my email. And in fact, all I need to remember is the password of my email, I synced everything, so when I log in to Gmail, everything automatically gets synced, and I have the doc where my seed phrase is saved.
I'd recommend that, it is convenient, easy.
Don't come here to cry if someone hacks you, and you won't be the first one to have it happen because he thought such things should be kept online. It's one of the worst ways to store seed/private keys, and I hope no one listens to your advice.