updating apps

Did you see my post above. Check out the part about What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071. Following this guide might take care of your problem.

If you changed to a new ID (didn't do a name change on your old ID), those purchases are tied to the other ID and can't be transferred. One option is to delete the apps/purchases made by the other ID and download them using the new ID if desired. If necessary, check your purchases history to see which apps/purchases weren’t made by the current ID. 

Purchase History Review.   

Or you can try to set up Family Sharing  between the IDs to keep access to your purchases.

Family Sharing.         

Family Sharing - Set up.        

You won't be able to do that. And, if you don't know the ID, note that it might be the Apple ID of a prior owner. See What to do when the Mac App Store shows a different Apple ID for software updates https://www.macworld.com/article/3267709/mac-app-store-apple-id.html This document refers to a prior owner, but is also applies to cases where a current owner's old Apple ID is a problem.

The document says (hypothetically): "Macworld reader Arthur is trying to download updates via the Mac App Store, but is stymied, because an Apple ID associated with the previous owner of the machine appears prefilled in the Sign In dialog and can’t be changed. He wonders what to do. Apps purchased or downloaded with another Apple ID will persist in prompting you for that account’s password when they need to be updated. Apple associates app purchases with the account that made the purchase. This includes “free” apps, because such apps can have in-app purchases, which would also be associated. If you bought, inherited, were given, or found on the street a Mac that was previously owned and not wiped clean, you can wind up with apps installed that are registered to a previous user."

Is it possible the problem Apple ID is that of a prior owner?

But, if you changed your Apple ID in the past, it also could be your prior Apple ID. That is the case Eric Root was talking about. Maybe the problem has arisen because when you changed your Apple ID you didn't follow this guide: What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071

When changing to the new ID, there may be some data loss, but you can minimize it. If syncing photos with iCloud, ensure Optimization is turned off in Settings/Your Name/iCloud/Photos and/or in Photos/Preferences/iCloud. Then make sure full resolution photos are on the device/computer. When signing out of iCloud, if asked whether you want to retain data, choose yes. Messages conversations will be lost if they are addressed to the ID. See the article below for other places that the old ID should be removed. See Winston Churchill's response in the below discussion. Also set up Family Sharing to keep access to your apps/purchases. 

 How to switch Apple IDs on your iPhone or iPad.      

How to transfer all files from one iCloud account to another.       

What to do after you change your Apple ID or password - Apple Support.      

Family Sharing.         

Family Sharing - Set up.