sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
sudo apt autoremove
sudo apt install update-manager-core
sudo do-release-upgrade

• Check cpu: lscpu
• Check memory: sudo dmidecode –type memory | less

If nslookup google.com gives error, there is problem. If nslookup google.com 8.8.8.8 gives no error, it means your default DNS is not working but things work when you specify a DNS. So specify a DNS permanently. Do the following.

sudo vi /etc/systemd/resolved.conf # open the systemd config file file
DNS=8.8.8.8 8.8.4.4 1.1.1.1 # add this line at the bottom in nano
sudo service systemd-resolved restart # restart systemd-resolve
cat /run/systemd/resolve/resolv.conf # check if the DNS's are there
sudo rm /etc/resolv.conf # delete this symlink
sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf # create new symlink
sudo service systemd-resolved restart # restart systemd-resolved again

And the problem should be fixed as a new nslookup google.com should show.