Of course, you could generate random phrases via the website which is generated by the browser cryptography API, and make an encrypted backup of it
https://bip39.org/#mnemonic.
I wouldn't recommend that anyone uses a website based javascript generator:
https://bitcointalk.org/index.php?topic=5324030.msg56590276#msg56590276[/quote]
Might be worth looking at the Bitcoin Core's RNG code for me but the RNG of JS which would be `crypto.getRandomBytes()` is already used for wallets like Metamask which more than a million people use to store crypto.