I read somewhere that encrypted home directory using encryptfs is not offered as option anymore with latest release.
Can I use a guest account on system with full disk encryption?
If you use full disk encryption - which is the only option in the 18.04 installer - you will not be able to use 'Guest'-accounts without giving everybody your encryption key. This is true not only for 18.04, but for every release before, if you used full disk encryption.
For 18.04 Canonical decided to not offer
eCryptfs anymore since the package is (or was) not actively maintained. Hence, securty issues and broken user experience could have a negative impact on the distribution itself, which clearly should not happen on an LTS release.
Also, in favor of better data protection, LUKS can be used to encrypt the whole disk.
ecryptfs-utils however was moved to Universe Repo, so you can install it from there.
To answer your question:
If you still want to encrypt your users home directories (i.e. on multi user machines) you'd be better off not enabling encryption during installation and then install the
ecryptfs-utils package later on to finally encrypt your user home directories.