Assuming there’s only one particle in the universe it would still have a temperature right? Not really. One (not quite universal) way to think of temperature

Assuming there’s only one particle in the universe it would still have a temperature right? Not really. One (not quite universal) way to think of temperature is as a measure of average energy per degree of freedom (linear motion, rotational motion, vibration, ...). This assumes a system where random interactions spread the energy throughout, exciting all these different energy states. In contrast, when you take your single particle and add some energy, there's no spreading of anything and no excitation of other degrees of freedom - the system doesn't 'thermalize', and no average emerges. Note that there are other ways to think about this, eg in terms of inverse temperature (thermodynamic beta), which is essentially a measure of phase space growth under addition of energy. Your single particle system will only exist in a single state no matter how much energy you add, so it's not really useful to take a thermodynamic approach...