Dear Alex,
Good day! Thank you for posting your query in our community.
Based on your description, you want to write a formula in the Calculated Columns on Sharepoint Lists. However, the column you need doesn't show in the Insert Column list.
As you mentioned, some types of columns are not supported in SharePoint Calculated Column Formula, like Person and Group type, multiple lines of text type, multiple choice type…
A possible workaround I can think of is that you could use Power Automate to extract data from the column, complete the calculation process in it, and then return the results to the SharePoint list.
Given this situation, we recommend you post this query on the dedicated Microsoft Power Automate Community, the members and engineers in this community are more experienced in this area. You will get a more detailed and professional answer to your problem there.
We appreciate your understanding.
Sincerely,
Jazlyn | Microsoft Community Moderator