Can’t help on the OS running as I’m not a Mac user but with regards to not getting the trial email, I understand this is often down to some email servers having the Steinberg trial address listed as a spam email address and so not letting them through.
I understand Gmail has been amongst those with this issue. If you an alternative email address(es) you might want to try those. Good luck.
Further to your question about whether your OS will run Cubase 9.5, you might want to ask it as a separate question in a day or two if you get no nswers as some who have the answer might not read the original post due to the title…you could modify the title maybe too?