You are correct. CO2 isn’t a poison. It’s just a gas.
Oxygen and Nitrogen aren’t poisons, just a gas.

However, while Oxygen & Nitrogen aren’t poisonous as found on earth. (Approx 20% & 80% respectively) Change those concentrations and it can be catastrophic to humans.
The same with CO2. Too much CO2 may eventually cause those CO2 loving plants to flourish too much, especially in the higher temperature environment they will be living in due to excess CO2 acting as a glass window completely engulfing the earth high in the atmosphere. (And it may affect the ratio of O2 & N2) The sun’s heat will be trapped in the volume below that “glass” enclosure much like your closed car windows in the summer heat.

This is happening right now on a smaller scale, but it is indeed happening. This doesn’t mean every portion of earth will be unbearably hot. Climates north & south may provide more favorable conditions.

The unknown is how the changing sea & air temperatures affect the jet stream (air) & Gulf Stream (water) . These are why the northeast US is comfortable in winter. (Yes cold but not like Europe) Slow down or stop the Gulf Stream (happening now) and the climate may get vey much colder in the winter and even hotter in Summer or the opposite (We just don’t know). You can observe the changes in the jet stream and Santa Anna Winds on the west coast climate. It’s causing increased winds and hotter temps out west. You see the increase in winds across the middle of US causing horrific storms. Much more violent that in the past.

I know this was a long way off from your initial comment but it is very much related to everything around you, me and virtually everyone on earth.