DIAGNOSIS A software setting is limiting the output, not a hardware failure. The prime suspect is the Volume Limiter feature, often enabled by accident via voice command.
FIX Disable the Volume Limiter. Say, "Alexa, turn off volume limiter." Confirm it's off in the Alexa app under Devices > Echo Studio > Settings > Volume > Volume Limiter. Then test volume.
IF THAT DIDN'T WORK Check the EQ and source. In the Alexa app, go to Settings > Music & Podcasts > Equalizer and reset it to flat. Also, the issue might be with your streaming service. Test volume with a different source (e.g., switch from Spotify to Amazon Music) to rule out app-specific volume normalization.
HEADS UP If you're using it as a TV speaker via optical input, the TV's own volume control and output settings are the master. Ensure your TV's audio output is set to "Fixed" or "Max" and not "Variable," which caps the signal.