I believe a fiber internet source alone does not inherently affect sound quality in audio streaming, as digital data transmission ensures bits arrive intact regardless of the medium. We need others to respond.
FYI - Fiber optics can reduce electrical noise, RFI, and EMI compared to copper connections by using light signals immune to electromagnetic interference. In high-end audio setups, this may lower the noise floor, improve timing precision, and yield a cleaner soundstage when using fiber media converters between network components.

