Opening Apex Legends Loot Vaults in Season 4 takes the same process as before. Sadly, Respawn Entertainment did not add any more loot vault locations leaving only three on the map.
This might be the biggest problem with them as Skyhook is a classic spot to find a Vault Key, but it's almost always useless as you have to travel so far south to use it. Respawn Entertainment definitely should have added on more vault up north.
How to Open Apex Legends Loot Vaults in Season 4
Just like in Season 3, players need to find a Cargo Bot flying around with a red light. If you find one, then you can destroy it, collect the key and go to any of the three locations. The mark will be gone if they were already opened, so be cognizant of that possibility. You also want to keep checking the map as you make your way there to see if anyone has opened it up.
Apex Legends usually changes at a slow pace. Season 2 barely changed the map from Season 1 and it wasn't until Season 3 before we got a new map. Season 4 looks to follow in the same footsteps. The changes are minor and it's probably kept simple so Respawn can focus on Season 5 with big changes.