Having to rebuy mw 2019??? [MW2]

So I’ve been seeing all over tik tok about the recent resurgence of mw 2019 and I loved that game so I redownloaded it (or so I thought) onto my ps5. I originally bought it for the ps4, and now it’s telling me I have to rebuy the game??? Is it because I only have the ps4 version? All my other games always just transferred over to the ps5 version without having to rebuy them. I have so much time invested into that game and I wanted the nostalgia but not for another $60.