It's always anyone's guess as to which machines will and will not support the next macOS version. Usually you can count on at least 4-5 releases to work, but some machines fall off faster than others, and then there are things like the 2009/2010 Mac Pro which i think only just now lost support (thought they were supported incompletely and only if you had a GPU that was higher than the base model to support Metal). I have a 2012 Mac mini that runs Catalina, so that's 8 years of support, but I highly doubt it will work with the next OS version.