Is Air Conditioned Rooms A Necessity in June/July

This is a good online resource to answer all your weather questions where ever you go
https://weather.com/weather/monthly/l/POXX0022:1:PO

Air Conditioning is used for more than just cooling down a room. AC allows you to close windows and shut out the bugs, keep the wafting cigarette smoke from the cafe below out of your room while you sleep, quiets the noise from loud bars and restaurants...

Since it’s very hard to know if a place will have a cross breeze, or any breeze at all, I would suggest AC. After renting vacation apartments for many years, the one place I couldn’t stay was in Lisbon the first part of June in 2015. The apartment was in Baixa and had no cross breeze. We lasted one night before checking into an air conditioned hotel.
Nazaré likely has the best bet for a cross breeze so close to the sea. If you forego AC, that would likely be the place to do it.

I preface this by saying I live in Alaska-so anything above 75 is sweltering to me. Also, even in winter in AK, we turn heat down to 62.
When we went to Ireland last summer we were on a music tour so I did not pick out lodging. None of the places had A/C.

While we did manage to sleep, it was a relief on our last night to sleep in a climate controlled room! Most of the older B&B’s don’t have A/C. What made things even worse, the windows were old fashioned and only opened up a bit, so a cross breeze was almost impossible! You wouldn’t think you would need AC in Ireland, but we would have loved it!
For the southern European countries, I wouldn’t consider going without it!

" Is it comfortable still without air conditioning in Porto at the end of June, beginning of July?"

Most of the times, yes. But sometimes it's impossible. I remember one year, I was returning from Algarve to Porto (I think, not sure, it was 2013) and at the 30th June Lisboa was 41 degrees (Celsius) at 1pm, and Porto, where I live, was still 36 degrees at 6pm.

For the benefit of my fellow Americans, 36C is over 95F.