@Marius-Swart
Alright I built a system to automatically update a SharePoint list with registration data from an external site. It required figuring out which rows were new and needed to be created in a list of 100,000+ rows. To work, you just need to have a set of values unique to each Excel & SharePoint record that can form a primary and a foreign key. For example, if each record in your Excel & SharePoint list have different emails, then you could use the email addresses as a unique id/key. My example will use names. Just make sure whatever you use as the unique id is cleaned wherever you use it (ex: use the trim function on email values to remove excess spaces or use the replace function on things like phone numbers to remove and spaces, parentheses, dashes, etc.).
First, use the Get items action on the SP list and turn pagination on with the maximum 100,000 setting to get all the records currently in your list.

If your list has more than 100,000 records, then you may need to use some of the methods I describe in this video to link together several Get items actions and pull several 100,000s of thousands of items.
https://youtu.be/l0NuYtXdcrQ
Then create the rest of this flow.

The Select action is just pulling the unique id/key values from SharePoint so they can be compared to the values in Excel.
Then the flow is getting all the records from Excel. you may need to turn the pagination on and set it to 100,000 for that too if you have a large table.
Then the Filter action is looking through every record from the Excel output and only selecting the records with unique values not already in the list of SharePoint unique values. The body from the Select action of unique SharePoint values must be reformatted as a string for the conditional to work. I have a way to compare array values that is more efficient, but it's more complicated and harder to explain.
Once you have the list of only the Excel records with unique values not in Sharepoint in the Filter array action, you can either use a Parse JSON action on the Filter array output to pull things into dynamic content or you can use the body of the Filter array action as the main set of values for an Apply to each loop and hand code item()?['ColumnName'] wherever you need values from certain columns.
And if you want to get more advanced and much faster with things like this then you can try learning the batch create and batch update SharePoint methods.
Batch Create: https://www.tachytelic.net/2021/06/power-automate-flow-batch-create-sharepoint-list-items/
Batch Update: https://powerusers.microsoft.com/t5/Power-Automate-Cookbook/Batch-Update-SharePoint-List-With-External-Data/m-p/1453405#M543