Thank you for your question!
To fix the ‘read-only’ status of a style, the first thing you will need to do is to upgrade the style. If you are downloading it from the online gallery (Forestry_En.stylx), when you add it to ArcGIS Pro you will be prompted to upgrade. Choose 'yes', otherwise it will remain as a read-only file.
Once you have upgraded the style, it should be shareable. That being said, yes this style unfortunately has some limitations with sharing as a web style. There are limitations with special characters because the ‘key’ fields within a style need to be a valid for a url. Since many of these desktop styles were from ArcMap, they contain these special characters since they came from before the web style days.
The work-around for this is, unfortunately, to manually change the ‘key’ for the effected style items. When you open the ‘share as a web style’ pane, after filling out the descriptions and tags, etc., click on ‘analyze’ this will give you a list of which symbols contain these special characters, so you can find them in the style and manually change the special characters in the ‘key’ field. (see attached screenshot.)
Let me know if this helps or if you need any additional information!
