Lately, I've been wondering about the meaning of a past tense verb connected to 上で, like in the 3 examples below:
What's the meaning of 過去形の動詞＋上で ?
It means "after doing 〜". Almost like
This is just a supplement to the above answer & comment.
Your question was specific to ~た上で (so I won't expand unless you expand the question) but FYI there are other different uses of 〜上. I found the following sentence (from one the Soumatome-goi series) helpful to remember: