So, its a little confusing so I want to restate and please bear with me, as I cannot see your data.
1. You have 2 lists in SharePoint (same site or different sites?)
2. You have a single column that you want to copy between the two
What is the Column Type please
3. You said - there is a guid_colum in both of those lists in source list this is a unique record
Do you mean, you have a text column in List1, that is the unique ID for that Record?
Curious, and totally cool to have a second one, but do you use the actual ID column (which is unique) for anything? just curious if we care about that
Ok
4. in the destination list there is multiple records with the same guid_column values
So essentially this is a 1-Many relationships between the Source and the Destination (for whatever reason, its cool just making sure I read that correctly)
5. of course I'd like to update all of them with the column_to_copy values.
So you have a Column in List1 (again please tell us the type), it has some value in it let's pretend it says IAM_Value1 and it maps to GUID 123456 (yeah I know that is not a guid)
Now in List 2 you have 1-Many rows where you have a Column (Text probably) that has the value 123456 for the GUID
- In that list you also have a Text Column which holds that value you want to copy
- Let's pretend 6 rows in List 2 match GUID 123456
You want the Text Column to be updated to be IAM_Value1 (which is my lame example)
If that is correct please do this.
Side note
What's weird about your statement is, I would find doing it in a Canvas App for instance super fast as you would simply do
ForAll(MyList1,
UpdateIf(MystList2, GUIDText = ThisRecord.GUIDText, { ColumnText: ThisRecord.ColumnText } )
)
But maybe I am misunderstanding.
Either way in Power Automate, the issue is you are going to have to loop through all the records to update them 1 by 1.
Also, please note, please share your flows in the future so we can help you fix what you did, as we are a support, free doing, teaching, helping, we don't like doing all the work for people as we don't have time.
Note: You didn't mention what would trigger this so I am going to write it as if you are going to do it 1 time and I'll mention doing it via Automation
Steps 1
1. Manual Trigger
2. Get Items - where you will use List1
3. Apply to each using the body/value Dynamic property output from Step 2
--in side the Apply to each
----Get Items - filtering List 2 on the value from the current iteration of the Get Items from Step 2, aka current item or item()
------Apply to each
--------inside apply to each
----------update item using the value from the Step 2 Get Items to update your column for every row pulled back in this Get Items
Bulk update
now if you want to avoid looping through them and depending on exactly what you want to update, you can look at using the Send HTTP Request to SharePoint Action to send bulk updates.
but you still have to find, and build the batch request before sending it, so its not going to remove ALL the steps above, its going to, at best, remove you calling update for each item and instead grabbing that data and shaping it into a bulk request with a whole bunch of stuff and limitations bla bla.