Hi Pavlo!
I hope you're doing ok given the circumstances. To the list that Fiona has shared, I'd add the Open GLAM survey by Douglas McCarthy & Andrea Wallace too: https://medium.com/open-glam/survey/home
That gives a sense of how many GLAMs have adopted open access policies.
Also, I'd suggest you get in touch with Iolanda Pensa from the Wikimedia Italy chapter: https://meta.wikimedia.org/wiki/Wikimedia_Italia. They took the CC GLAM Certificate course and their whole team produced a ton of wonderful visual materials (slides & infographics) that explain the benefits of open access for GLAM institutions in a very straightforward way. Most of them are uploaded here: https://commons.wikimedia.org/wiki/Category:Creative_Commons_GLAM_Certificat...
cheers, scann