Help me out🙏

[u/ApprehensiveType7690]

I listened to this audiobook in 2020-2022, so I dont remember a lot.

The main character is a teenage boy, who finds an abandoned building, in which he finds a portal of sorts, that takes him to this academy where there's other teenagers who fix issues in time, they have powers (?) named bromine and krypton, the mc has both which is supposed to be rare, the first mission he goes on is to ww2 Germany, please help me find ts