https://www.gamespot.com/articles/pokemon-go-last-chance-to-catch-legendaries-latios/1100-6459368/

Pokemon Go's latest Legendaries, Latios and Latias, have been a staple of Raid Battles for the past couple of months, but the Eon Pokemon won't be around for much longer. Both Legendaries will only appear until June 5, making this your final opportunity to capture one if you still haven't.

Like most other Legendaries, Latios and Latias can be encountered in Raid Battles at Gyms, although each one is only available in specific regions. After swapping locations back in May, Latios can be found in Europe and Asia, while Latias is appearing across North America, South America, and Africa.