According to the uefa website:
The Resale Platform will be open until the end of March 2024. After March, there will be no further opportunities to resell tickets.
I just logged on to my ticket portal account and on the right had side it has an option for 'Resell Tickets'. When I click on it I can see my tickets and I can put them up for resale if I want.
Looks like you can go on now and check. I've just logged in here https://euro2024-fans.tickets.uefa.com/ and says unsuccessful for the games I've applied for.
I've had this for 3 bookings I've made for the Euros. I reported it the first time to Booking.com and they said they'd investigate, haven't heard anything since. I didn't bother then next 2 times, I just ignored it and hoped it was a scam.