Frustratingly, this is not as universally supported as it should be.
Back in 2018 I bought a plane ticket from Eurowings and I gave them an email address with that pattern, and while they were happy to accept the email address on the booking page and take my money, the ticket and login systems didn’t, and I had to get a refund and a much more expensive last-minute ticket at the airport.
(The customer support person also managed to spell my name wrong when I contacted them).
Back in 2018 I bought a plane ticket from Eurowings and I gave them an email address with that pattern, and while they were happy to accept the email address on the booking page and take my money, the ticket and login systems didn’t, and I had to get a refund and a much more expensive last-minute ticket at the airport.
(The customer support person also managed to spell my name wrong when I contacted them).