@Gfran999 You can customize list forms using Power Apps and use custom logic to auto populate columns based on selections in other fields - this will auto populate and update column values immediately.
Another option is to run the Power automate flow on item creation/update to auto populate columns based on other column values - there will be some delay in seeing the auto populated/updated values till flow run completes.
Please click Mark as Best Response & Like if my post helped you to solve your issue. This will help others to find the correct solution easily. It also closes the item. If the post was useful in other ways, please consider giving it Like.
For SharePoint/Power Platform blogs, visit: Ganesh Sanap Blogs