Hi! Tim I notice that this is your first post in the forum and just wish to say welcome.
We just wish to get some additional information so we can make a clear and focused response. This is a user to user forum so the responses you will receive here are from other users like yourself.
As a point of clarity, you stated: "I can't figure out why they won't open CR3 files". Well, the reality is Lightroom is not a file browser so it does not open files per se. You first have to import the files into the Lightroom Catalog so you can start working with them. CR3 files are raw files from Canon digital cameras and Lightroom has to first provide support for the particular camera model before it is able to import the files.
Please see the screen capture for more info.
Regards, Denis: System iMac mid-2015, 5K 27” monitor, macOS10.15.6: LrC 9.4, Lr 3.4.1, Ps 21.2.3, Camera OM-D E-M1.