and welcome to the Community,
to be honest, i’m not 100% understand the final goal, and why just don’t copy-paste full list from excel.
anyway, i suppose you need a list of unique country names from both sources.
just add whole excel list to the countries field, choose “customize field”, find “single select” but don’t press “save”, you will have a list of unique values, that you can ctrl+c (choose “cancel” to avoid field change, then paste that list where you want.
I usually use it as “lifehack” similar to Excel “remove duplicates”
For example, I just took a random list of 10 “A” countries and make some chaotic repeats.
Two more contained in other list
other scenario - you need to know exactly which countries from excel are not present.
create empty second table. link countries table to it, copy-paste countries to linked field.
You will get unique countries list in second table. put some mark to the second field for all list.
then add excel data and check for unmarked.
here is a pic of 2 tables to explain better. that approach with second temporary table also may help to quickly find duplicates, number of values in a field (by adding count in second table and put as lookup in first) and so on. the key is - when you fill linked field by copy paste, airtables tries to find that value in linked primary field, and if not, it creates additional record.
Second temporary table (i just forget to remove default first three empty records)
I hope this example will be useful for other possible tasks