Will the quality of copied images be lower than the quality of the original ones?
The extension provides the functionality to select the required quality for the particular pattern (100%, 90%, 80%) in Amasty > Google Page Speed Optimizer > Image Optimizer > Image Folder Optimization Settings:
Additionally, you may also set the required compression quality for images (WebP and AVIF) in Stores > Configuration > Amasty Extensions > Image Optimizer > General Settings. The quality level can be adjusted on a scale from 0 (worst quality, smaller file) to 100 (best quality, larger file) for AVIF and 99 for WebP.