RE: Business Process Flow Not appearing on forms
Hello all,
Just coming back to let you know the resolution. It was none of the above items, as I had checked all of those already. I submitted a ticket to microsoft and it was a bug that they are patching. If you're having the same issue, the resolution from Microsoft is below.
I was able to replicate the issue and I found a bug that happens when the Accent Color is not defined in the custom theme.
So I confirmed that the theme in the organization with the problem was indeed undefined:

When I changed to #000000 and published the theme, the issue was resolved.
This bug was already fixed and the release will come to service update 9.2.23044, so the ETA is May 26th for NAM Geo. We recommend you to please use the workaround until then by adding the accent color for now.
I also would like to inform you that we still have limitations around using custom colors with this modernization:

Modern, refreshed look for model-driven apps (preview) - Power Apps | Microsoft Learn
Hope that this helps you! Please let me know if you have any further questions or concerns.