I agree that the use of an additional word in the seed phrase is a good solution to increase security damage, but I would recommend having multiple backups available anywhere in the world and anytime.
What is recommended today may become necessary in the future, because if we want security, we have to invest a lot more than $50 in a hardware wallet and 24 words on a regular sheet of paper. As far as I can see, opinions are divided between those who suggest encrypted files saved online or on some medium, and those who still stick with multiple backups on paper/metal plates.
I agree that in case we use backups on paper/metal or any other more durable material, we need to use extra word (passphrase) as extra security in case someone if find our backup. Of course, in this case one should be intelligent and separate the seed words from passphrase, and take into account that weak passphrase is not good move since it is subject to brute force attack.
The whole point of this topic is to start acting more responsibly towards what we are protecting.