I did a little research:
The county can only be omitted if there is no second place of that name in Ireland or if an Eircode is provided.
However, the Irish Eircodes have only existed since 2014 and are not mandatory. Many companies still do not use them at all. So you would have to search for the code on the internet every time. It's a bit laborious, but it should be OK.
If you search for the Eircode using my example address from Apple, you will find that there are actually different Eircodes at this address because every single building in Ireland has its own Eircode!
Addresses without any understandable location information can occur. A correct Irish address is also:
Apple
T23 YK84
Ireland
Or even just:
T23 YK84
Ireland
Or with all of them at once (the code always comes after the location in Ireland):
Apple
Hollyhill Industrial Estate
Hollyhill
Cork
T23YK84
Ireland
Whereby this spelling is also correct:
Apple
Hollyhill Industrial Estate, Hollyhill
Cork
T23 YK84
Ireland
The spelling I wrote yesterday in this thread, on the other hand, is unusual (Hollyhill, Cork) If the address is written in one line at the bottom of a letter, it is easy to get the formatting wrong. (Ialso come from Germany and have to look everything up.)
Eircode search (works both ways): https://finder.eircode.ie/#/
https://en.wikipedia.org/wiki/Postal_addresses_in_the_Republic_of_Ireland
As I only read today, it is probably better to use the EU-wide standard Peppol BIS Billing 3.0 anyway when sending invoices to other EU countries: https://docs.peppol.eu/poacc/billing/3.0/bis/
Maybe something you could include?