To be honest, now there is less and less confidence in any sources in general every day. I already store it simply on a piece of paper.
good friend, the right choice to save on a piece of paper is safer, if you save it on android it can be hacked, it's not safe. I've always kept the key on the bag until now it's still safe and there are no gaps to be hacked.
keys stored on paper are also safe, but the paper will be destroyed if exposed to water, keep the paper not exposed to water, I recommend that besides storing it on paper, you can also store your keys on a cassette because the tape is also safe, don't just store it on the top paper.