Can't get gmail account to be authenticated on Mail app because of Safari issues

Recently I downgraded from Catalina back to Mojave and my Safari browser stayed Catalina version, so now it is incompatible with Mojave and doesn't work. When trying to login my gmail account to Mail app, the pop up window for authentication comes up, it wants to open through Safari. Is there a way to change the pop up browser to Chrome? In Preferences/General Chrome is set as my default browser, but all the pop ups still open through Safari.... What should I do? I don't want to reinstall OS again, nor do I want to upgrade back to Catalina...