I can't change my timezone

Hello, I'm writing this message to inform you about an issue I have.

I want to publish a one-shot on my page, but for that I need to fill in the timezone. However, nothing appears when I do want to put my timezone in: the field where I'm supposed to put my timezone is just blank, and it does the same when I want to do it on my page settings.

Here's a picture: https://ibb.co/DgRZPgCs

Please inform me if you have a solution for that.

Thank you very much,
Beemonki