In Chrome extension, while the font does distinguish between O and 0 and l and 1, it is quite subtle, and if you don't see both characters, you can't readily tell which is which. Why not use Consolas, monaco, monospace? It's just not that hard.
Thanks for reaching out. I've passed your feedback about the font/readability of LastPass in across LastPass products along to our development team to see if this could be changed or updated in the future to better distinguish characters (especially similar characters) between one another. The LastPass app for iOS does currently show passwords in your Vault in a different font and colour for each different type of character when viewing a password, so this would be a great feature to have on other platforms as well!