Can you check out my post here that I replied to just this morning. They were just trying to fill a specific field, but the concept still applies.
https://powerusers.microsoft.com/t5/Building-Flows/Add-Row-Step-in-Excel-Business-Online-Missing-Dynamic-Content/m-p/2338197#M259970
The dynamic content is there, you just have to manually address it.
Sometimes Power Automate is trying to be helpful by limiting options based on field type. For example if you want to insert data into a datetime field, PA won't show dynamic content that are string/text type.
This isn't always helpful, and PA isn't always accurate.
You can manually put the 'dynamic content' into an expression and it should work.
The easiest way to manually put in dynamic content is to add a Compose step. The dynamic content should be available to put into that Compose. (If it is not available for the Compose then you have a different problem.)
Highlight and copy the dynamic content and past it into like a text/notebook.
Copy Dynamic Content
Paste Dynamic Content into Expression
Make sure you remove the '@{}' from the copy and pasted dynamic content.
This may seem like a hassle, but I have to do this all of the time when using expressions.
