It is important to backup your seed phrase but some people said the backup is not good online but which is true because we have seen how hackers was able to see some people seed phrase online and steal their coins.
It's never been ideal to store your seed phrases online whether it's on a cloud storage, email or spreadsheets or whatever that's online even on personal messages on social media platforms.
But I have been thinking recently that how can people in countries with natural disaster be able to backup their seed phrase offline? An example is the flooding that occured in Pakistan like 2 or 3 years ago that submerged 1/3 of the country under water. Even if you backup your seed phrase offline in many locations, it is possible that kind of flood can lead to permanent loss of your offline seed phrase.
Aside from engraving it with steel, those that are still into written forms through paper can use plastic envelopes or anything that are water proof for the covering of the plate or card where you've written your seeds. I know that it's not 100% fool proof but each ways have its own cons and it will depend on the situation of the owner on how to keep their seeds safe and the storages they use.