If a US resident (not citizen) only works outside of the US (remotely), and resides in the US for the whole year, do they have to file taxes?

In April 2024, I was able to bring my dad to live in the US using the IR-5 visa. His job is outside of the US and he is still working there remotely. He's planning to continue working remotely until the end of the year. Assuming he doesn't get a job based in the US this year, does he have to file his taxes? If so, what does he need to do to file his taxes?