I do not know what OS is, but I sign documents on my Mac, iPhone, and iPad. My iPhone and iPad have the current Versions of the operating system. MyMac has not been upgraded to Catalina. However, if it was not Catalina compatabile there would be many posts in the forum complaining and that is not the case. It is more likely a browser issue and incompatible extension issue. They can post here with details and get help with the issue. Since they have access to non-Apple devices they can sign the contract if they wish.
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