Within Portugal, yes, legal until June 30, but it’s a national regulation, not necessarily binding or honored by other Schengen countries, as has been discussed multiple times on the forum in the context of travel.
This is likely going to be a problem. I’ve traveled twice on the edge of permit expiry and in both cases the immigration officer at entry looked at the expiry date, said “you know this expires in x days?” “yes” “how long are you staying?” “x - 3 days” and in one case I showed the return flight details. The interactions were cordial but I don’t know how things would have turned out if I had given an answer of “x + 1” days.
The checking of permits in intra-Schengen flights is random. Some airlines/airports definitely check it. Like Faro - every single time I fly out of Faro to Schengen destinations, Tap Air and Transavia check permits, and I’ve seen people with invalid permits being denied boarding.
If it was me I wouldn’t risk it. Unless maybe I was entering/exiting from Portugal itself and I armed myself with all the necessary documentation.
Some airlines explicitly say on their websites that they recognize the Portugal permit extension (eg Emirates does iirc). Try contact the airline to check their policy before buying tickets.
Even passing thru airlines, you will go thru the security check. For some airports, the security guy checked the passport and then asked for the resident card. That’s what I’ve experienced in Istanbul airport. There were several layers of security that I had to show my resident card. Without of having valid card, risk of being denied boarding or kicked out is significantly high. So good luck to those third world passport holders who travel with expired GV resident card.
So there are two distinct entities here: airlines and immigration at the port of entry.
Airlines denying boarding isn’t too bad, but being denied entry by immigration officials at the Schengen port of entry is a much bigger deal. It’s going to get stamped on the passport as an entry refusal, recorded in SIS, and likely to impact future visa applications to the Schengen area, and having to explain every time why it happened.
If you’re flying “direct” into and out of Portugal, i.e. your first/last Schengen touchdown is in Portugal it might work, if airlines cooperate, because Portugal immigration ought to recognise the validity of the permit beyond notional expiry. Even so, travelling out of Portugal within Europe on an expired permit is highly inadvisable.
They do check - it is not universal or even common, but possible. Germany, Netherlands have started some amount of checking at land border crossings.
Flights departing Faro always check for valid residence permits. In some countries (definitely in the Netherlands, pretty sure others we well) the police can, on suspicion, or at a traffic stop or border crossing, ask you to show ID and proof of legal residence status. If you possess a valid permit but are not carrying it with you, you can get fined.
Even if it is technically legal, I am not looking forward to explaining the minutiae of Portuguese government declared extensions to Dutch or German or French police if I get involved in a traffic incident.
I wish online renewals would start or at least portugal issues Schengen visa. My son is in the US and since his last Schengen visa was 10 years back when he himself was only 10 years old, he can’t just mail-in his application and will have to fly to the nearest consulate for his visa. The Portuguese Consulate is just disregarding his Golden Visa and Citizenship application. And no guarantee of a multiple visa either.