That is not recommended because 20.04 LTS is already end-of-life and therefore out of support. It might be better to install 22.04 LTS
That is a well known nVidia problem which also crops up on 18.04 and 20.04 and is nVidia driver related. See this:
https://ubuntu-mate.community/t/i-get-a-black-screen-when-booting-from-usb
https://ubuntu-mate.community/t/black-screen-issues
https://ubuntu-mate.community/t/black-screen-after-boot-on-18-04-with-nvidia
https://ubuntu-mate.community/t/black-screen-after-changing-graphic-card
https://ubuntu-mate.community/t/black-screen-missing-login-screen
https://ubuntu-mate.community/t/black-screen-no-login-prompt-after-latest-nvidia-update
https://ubuntu-mate.community/t/get-black-screen-lightdm-cannot-start
Have you tried NOT using the closed source proprietary nVidia drivers and use the open source free Nouveau drivers instead ? They are probably a much better fit for a 9400GT
(b.t.w. Open source drivers are almost always qualitatively better than their proprietary counterparts).