The only reason why the next button stays disabled (grey) is when the entered mnemonic is not valid, either contains invalid words (not in the list or wrong spelling) or has an invalid checksum (could be because of wrong word order or one or more wrong words).
The only other reason I can think of which the next button stays disabled is if you enter a mnemonic in the wrong window (like when recovering using "master key" or recovering a 2FA wallet with a standard seed).
If you are sure about being in the right window and also not having any typos then your only remaining option is to brute force the mnemonic.
Start by looking at your seed phrase, for example if you have a word that is repeated twice there is
a small chance that it was a mistake and you wrote it twice. That's a candidate word for change.
Also look at the word list, there are similar looking words that you may have written wrong. Like act/actor, aim/arm, space/spare, etc. Link to word lists:
https://github.com/bitcoin/bips/blob/master/bip-0039/bip-0039-wordlists.md