I've got a bunch of web3 domains via Unstoppable Domains and I always wanted to import them into my Metamask wallet (vanity, I know). I've fond a tutorial here, but it's a bit outdated. I did manage to import them and the steps I did are below.

Prerequisite

First, you need to claim your domains

On Unstoppable Domains

Go to one of your UD domains (profile):

Scroll down to "Token Gallery":

...and click on the Configured button. You will get a Token gallery (d'oh!):

Click on the domain you want to import, laurivan.wallet in my example. I got a pop-up with details:

Click on one of links (like View in Marketplace). Normally, this should open in opensea and you should see even more details.

Take a note on which network is your token. Mine is on Polygon:

Keep the tab open in your browser.

Metamask

Open Metamask and maximise (click on the three vertical dots and then on Expand view):

Select the proper network (I usually keep the wallet on Ethereum Mainnet):

Select the "NFTs" tab:

Click on Import NFT:

You will get a popup/dialog box:

Now, switch to the OpenSea tab and note the URL:

  1. the 0x.... in the URL is the Address
  2. the numeric value after it is  the Token ID

You have them also under Details lower in the web page:

Just copy them in your Metamask popup and click Import. Now you'll have the NFTs in:

Rinse and repeat for your other domains.

HTH,