75°C is fine. Even while just gaming. Chips have been getting hotter. They have built in thermal targets, so it'll boost as high as in can within thermal limits.
More case fans can help a bit. Your CPU cooler should be up to the task of cooling the 10900K. If you want marginally better temps, you could try switching out that old NT-H1 from the Noctua NH-D15 for Thermal Grizzly Kryonaut.