Kingil Hey !
First you need to know, it's that process is espacialy for french national. I have no idea if it's same for other nationality ...
But I guess it's really similar for EU countries !
1/ I'm in a non offical couple (no child, no welding, nothing official), so as proof, they ask that both person of the couple do a declaracion jurada (sworn statement) :
- in Argentina it's with an escribana(o) and 2 witness (it can be from familly)
- in France we can do it in the city Hall with 2 witness, then we have to legalize it (we call it apostille), so basically, it's the governement with stamp your declaracion which mean that it's offical for international.
2/ when this is done, they ask a negative PCR test done 72h before take your flight.
3/ you need ther DNI or passporte copy of your partner
4/ heatlth insurrance that cover you for covid
5/ you need flight ticket way and back (for french we are allowed to stay 90 days in argentina then we have to come back france)
6/ a note which explain the reason why you come to argentina (famillial reunification, address you go, your phone number, partner name + DNI, ect...)
7/ you have to register your trip on the migrationes of argentina in the 48h before your trip (https://ddjj.migraciones.gob.ar/app/ )
All these informations are avalable on the french embassy website, so I guess you need to ask you own embassy if it's same or you need special things
Where are you from ?