I'd spend 100M in a month easily. Especially after I've bankrolled GrapheneOS, Ladybird and all my favourite FOSS projects. They also didn't say anything about charity which IMO isn't gifting. Once I feel like I've sufficiently contributed to society I'd buy a 50ft sailboat, pimp the shit out of it with solar and fuck off forever.

With the billion I'd establish a fund that pays out monthly to any projects I deem worthy and funds all food banks in my local area indefinitely.