Also, the bit where the kid is just scrolling / playing on his device while his dad yells at him is some kind of crazy fever dream from right now.
The first is the literal one: no fertility, no babies being born, authoritarian government, etc. Not implausible, in my opinion --- imagine if COVID made people infertile? I still remember the lockdown days, when the first strain of COVID was prevalent, and people weren't sure if it would give you permanent brain damage.
Then there's the more metaphorical take, and I think this is the one people point to when suggesting the movie represents our reality. It takes place in a dystopian future with extreme income inequality --- think of Theo's (the main character) cousin living in the Tate Modern, and Theo being driven to see him in a fancy car, past parks with zebras and camels. Most people in England see a world full of hate, violence, and lack of purpose.
The extremely bleak lack of purpose, though, is the key part. This is a future that also implies there is no future. It's why you have ads for Quietus (the suicide system). The infertility isn't just literal infertility; it implies a deep hopelessness; that there is no future at all.
Theo and his cousin are also relevant here. Theo asks his cousin how he thinks about the future, given that humanity is expected to die. The response is "I don't think about it."