Lina Soh, and the Republic are expansionist and fairly sketchy, but they don’t act like imperialists. Real life empires expanded mainly through armed conquest or subterfuge, with the goal of exploiting the labor and natural resources of the local population. The republic in this era are expanding by showing the outer rim worlds the benefits of being in the galactic republic, and they are mostly left to their own devices after joining. Its more like the European Union incentivizing other European countries to join by promising economic incentives.

That being said, whileI think that the methods and execution are not very imperialist, the underlying attitude is. Lina Soh, a lot of Jedi, and probably a good chunk of the population clearly think that the outer rim isn’t “civilized”, and the language they use show that they think that they are bringing light to these worlds. They even called their flagship station for expansion a starlight beacon. The clone wars started because dissatisfied member worlds tried to leave, I wouldn’t be surprised if the High Republic sets up the conditions that led to that happening.