I use gradients in diagrams which can only be read-only in Visio's web client, I assume this is still unchanged.
Can users however now comment on these read-only diagrams in the Visio web client?
I see on the Visio roadmap that the web client has been improved for commenting a few months ago:
Visio: Enhanced collaboration experience with modern commenting
Set your stage with a richer commenting experience that provides a modern UI and is consistent with other Office apps.
Feature ID: 63007
Added to roadmap: 5/27/2021
Last modified: 7/1/2021
Product(s): Visio
Cloud instance(s): GCC High, GCC, Worldwide (Standard Multi-Tenant)
Platform(s): Web
Release phase(s): General Availability
https://www.microsoft.com/nl-nl/microsoft-365/roadmap?ms.url=roadmap&rtc=1&filters=Visio%2CLaunched