People who vaccinated and have licenses can join the match. If the government allows open stadium, with big crowd, they will ask those vaccination license. But it is still risky, you can still be infected even you are already got 2 doses of vaccine.
As far as I know, Vaccine do not make recipient immune to viral infection and they are still at risk of contracting it even after getting 2 doses. This may have to get the attention and consideration of the government before giving permission to the supporter to fill the stadium. If the government give permission, health protocols and social distancing must also be applied to minimize the number of transmission.
Thanks to vaccination and much better numbers in europe, there is a good amount of places that accept the fans in the stadiums, I do not mind it honestly, obviously there is a good amount of games that I watched which I believed was better without any fans, there are "derby" type of situations which means it is really worse with fans because they create a chaos, this way there is none.
At the end of the day there is a good amount of players who ask for fans and that is what matters, if the players want to see the fans and if the organizations need the fans for the money for it, then there will be fans because that is the people who they are trying to appease and that is why there will be some fans, not full stadiums but there will be some fans. I wouldn't really mind if the game was like zero fans, just friends and family, like maybe 200 at the most.