Navigate to and ensure 24-bit recording is checked.
Many users confuse version updates with feature updates. Version 10.4.8 did not fundamentally change the audio processing engine to make it "higher quality"; instead, high-quality output in GarageBand depends entirely on user settings and external hardware. 🎛️ 2. Unlocking "High Quality" Audio in GarageBand garageband 1048 high quality
Do not use "Graphic EQ." Use the (located under "Audio FX" > "EQ"). This is a parametric EQ with a high-definition 32-bit engine. Navigate to and ensure 24-bit recording is checked