Same gas, same compression ratio, two completely different final temperatures — because one process lets heat escape to hold temperature constant, and the other lets none escape at all.
Isothermal and adiabatic are the two opposite idealized limits for how a gas exchanges heat with its surroundings during compression or expansion. An isothermal process allows unlimited heat exchange with the surroundings, specifically in order to hold temperature constant — which in practice requires either a very slow process, giving heat all the time it needs to escape, or excellent heat transfer (a jacketed reactor, a large surface area, a thermal reservoir sitting right at the boundary). An adiabatic process allows zero heat exchange with the surroundings — perfectly insulated, or simply happening too fast for any meaningful heat transfer to occur in the available time. No real process sits exactly at either extreme, but they bound everything in between, and knowing which one a real compression is closer to changes the temperature prediction dramatically.