I can confirm this. It only affects UE Portable. UE 18.00.0.1034 has the information, and UE Portable does not.
You are also missing a checkbox under Version backup for: On automatic save, as well as the box to enter the maximum number of saves for Version Backup.
I only just installed both this morning (I've been using UEStudio), and noticed the difference between the 2 when trying to set them up side by side to configure them the same. I suppose I could have configured UE, then copied the INI to UE Portable, but as some of the features are disabled for UE Portable, I wasn't sure if it would cause problems, so was going to come here and ask first.
I know there are supposed to be several features "disabled" in the portable version of UE, but am not sure if this was supposed to be one of them. It seems odd that the spinner button for the maximum number of saves is visible, but disabled, but the actual text box that contains the number is absent. It also seems to me that if you should be able to specify the number of backups if you are using Version Backup.
I'll have to shoot an email to IDM to ask about their intent on this. Most likely, this is just one of the features that just aren't feasible or easily handled in the portable version.