Since patch 1.07 this no longer is possible. Planets without animals no longer have the 100% completion box and therefore no option to upload it.
Is there perhaps an easier way of exploring a planet completely?
I spent a lot of time on my starting planet and the first I visited after that. Only to find out right afterwards that some planets do not have any species and you immediately can upload the 100% completion to update your milestones. From my experience these usually are moons.
Of course this does not give any Units for reward. But making money is much easier by farming resources anyway.
To upload the 100% completion and get the Journey Milestone updated, you need to hover the pointer over the box which shows "100%" and press ╳ (on PS4), not ▢. That's the same when you want to upload the 100% for a planet which has species. You do not get the Units rewards automatically just by discovering all the
Sorry, german screenshot...