I thought of something that would explain slowness, and where being on 2.4 GHz WiFi would make it even slower…
Catalina seems to default to having your desktop and documents folders being on your iCloud Drive. That can be convenient if you’re using two computers and want to carry on working on something without having to upload files all the time. But, it’s not so good when you download a large file (which then immediately gets uploaded to your iCloud Drive), or if you’re working on large SketchUp files that you think are on your local drive, when they’re not.
I was using Catalina from its first beta, and it took me some time to notice the slowness (I have fast WiFi at home and at SketchUp). What gave it away eventually is that it was taking a long time for the recent files thumbnails to draw, because I had been testing several large files that I thought were in my local downloads folder.
Anyway, there is a setting where you can turn that option off. Things become faster then.
