What Malthus wrote about was basically the lived experiences of those around him for basically all of what he knew of to be recorded history: improved farming meant more people, not happier people.
Now, I'm not qualified to even judge if Jared Diamond's even fair let alone correct, but he wrote in Collapse (2005) that the Rwandan Genocide was brought about in part due to excessive population pressures, that it "illustrates a case where Malthus's worst-case scenario does seem to have been right."
On the other hand, it also seems plausible to me that widespread access to contraceptives may break the assumptions behind Malthus.
We had some impact as hunter-gatherers at 10M population, probably made some species extinct from hunting. If I assumed c. 1940 tech was the limit and wanted to minimise human ecological impact, this population would be the maximum sustainable given CO2 emissions.
Conversely, if we put submarine cities in deep water, powered by PV on the surface that are ready to withdraw when storms come[0] and feed ourselves on the most efficient foods we already know how to grow in sealed environments, we could probably support trillions of people… but at that level we might possibly need to find some asteroids rich in, IDK, phosphorus or something.
I have seen larger maximum population numbers, but they're for scenarios where you fairly strongly disregard the ecology — if you're willing to do weird stuff like putting up an L1 sun shade to block wavelengths of sunlight that serve only to heat us up because they get fully absorbed by the atmosphere, but somewhere in the 10-100 trillion range our direct heat emissions become dominant.
[0] ignore the expense, this is a thought experiment
There is but there is a 7/8ths probability that you're not going to like the answer.