I can't find find the "Change look" option in my site settings, do I or the Administrator need to activated some feature?
Currently there's an issue with the site themes. Maybe your question has to do with this issue?
See this twitter converstation for more details. https://twitter.com/wictor/status/1034811057397751809
If this is the same issue, the workaround is:
Sorry everyone! We're aware of the issue and actively investigating. I will note that as a workaround, if you access the "change the look" panel from the documents library you will be able to access your themes (both SharePoint ones - if enabled - and any custom ones)!
To change the theme, you need site owner or design permissions on the site.
if you are the Site Owner and still not able to see the "Change Look" Option then raise a ticket to MS.
here is MS help refrence for "Change Look"
There can be a permission problem if its only you that cant see "Change the look". Microsoft writes on there support page:
Note: To change the theme, you need site owner or design permissions on the site.
Which means that you either have to be a site owner/administrator or have the Administrator provide design permissions to you.
Have a closer look on the support page provided by Microsoft. Change the look of your SharePoint site