Many web pages claim that when you install 10.13 on an SSD, you have an option to convert to APFS. Many others claim that when you install 10.13 on an SSD, you will be converted to APFS whether you want it or not.
Neither was the case for me. I have an internal SSD that upgraded to 10.13 and continued to the current 10.13.6. Default disk utility knows it is SSD and HFS+ but will not convert it. Recovery partition won't convert it either. And in none of my upgrades was I ever offered the choice.
I don't want to erase and do a multi-hour install, then have to do a multi-hour restore from backup. Especially since I recently did (10.13.6) from recovery partition and it did not convert.
One page said you can't do it on your boot volume till 2017. But 2017 is long gone.
SSD was in this refurb when I bought it from the Boston Apple store January 2017. I used Migration to put apps and accounts on it, Software Update since then. Never used FileVault nor RAID nor Bootcamp.
MBP-WWG:Desktop Admin$ diskutil list /dev/disk0 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *1.0 TB disk0 1: EFI EFI 209.7 MB disk0s1 2: Apple_CoreStorage ISSD 1.0 TB disk0s2 3: Apple_Boot Recovery HD 650.0 MB disk0s3 /dev/disk1 (internal, virtual): #: TYPE NAME SIZE IDENTIFIER 0: Apple_HFS ISSD +1.0 TB disk1 Logical Volume on disk0s2 1687664E-6E25-4DBD-9293-A6B0E4D90B0A Unencrypted MBP-WWG:Desktop Admin$