I googled global waste per year. Looks like it's on the order of 2 billion tons per year. Leaving room for 100% growth, and assuming a density of 1 (less dense = more space required = worse), we'll need 4 billion cubic meters of landfill per year.
That's a cubic mile of garbage!
But that doesn't seem all that catastrophic either - if you spread it out to a hole 1m deep, it'll be 63 km on a side. 5m deep = 28km on a side. That's a lot, but it doesn't seem like the highest ecological priority. If it's practical to compress before dumping, it will be even less terrible.
To get really controversial the highest environmental priority is atmospheric co2 and landfill space doesn’t have a scratch on it in terms of harm.
Plastics and other carbon containing substances buried underground sounds terrible at face value but the thing that should really make you worry is the amount of carbon released into the atmosphere. Atmospheric pollution can often coincide with the amount of trash you create but in general if your focus is on landfill rather than atmosphere you’re focusing on something that doesn’t have a scratch in levels of importance.
In fact if we can find a way to landfill co2 rapidly in a net co2 negative way that may be our best hope right now (repeatedly growing and burying large amounts of biomass for example).
Geoengineering could maybe bring temperatures back down, but you can't just replant an old growth forest and out all the old plants, fungi and animals back.
If microplastics are behind the fertility drop, reverse flynn effect or obesity crisis they would also be more important in the ~100 year timeline.
A lot of that waste is organic and will degrade over time. And ultimately all that "garbage" was extracted from the earth in the first place. It's like that Monty Python quote "what did you start with? Nothing. What did you end with? Nothing. What have you lost? Nothing!"
That's a cubic mile of garbage!
But that doesn't seem all that catastrophic either - if you spread it out to a hole 1m deep, it'll be 63 km on a side. 5m deep = 28km on a side. That's a lot, but it doesn't seem like the highest ecological priority. If it's practical to compress before dumping, it will be even less terrible.