When using lookup columns that have been created at the site collection level and used in subsites these lookup columns will not be available as the Web of the list and the web of the column don't match.
For more detail see here:
Thanks for your sharing, the issue is confirmed on my side.
I would put this issue to my product team, then check if the issue would be solved in future. If the issue is solved, I would reply here.
If you have any other questions about Microsoft Flow, please feel free to reply here. We would provide a proper workaround for you.
The original report said "solved" and click here for solution, i clicked "here" and there isnt a solution. Why the hell not? I want to be able to access site columns in a parent site, when creating a flow on a list or document library in a subsite. This simply CANNOT be by design. Get it fixed and urgently!