Connecting to Ubuntu 18+ Remote Desktop from Mac

[Step 1] Ubuntu: Install Vino Server

Install the Vino server:

sudo apt install vino

[Step 2] Ubuntu: Eenable Screen Sharing

As instructed in this page, go to Settings→Sharing→Screen Sharing and check the option Allow connections to control the screen as well as Require a password if desired (recommended).

[Step 3] Ubuntu: Disable Encryption

Run the following to disable encryption so that your Mac can connect via VNC without an compatibility issue.

sudo gsettings set org.gnome.Vino require-encryption false

[Step 4] Ubuntu: Start Vino Server

Then, you can run the remote desktop sharing server (Vino server):

sudo pkill vino
sudo /usr/lib/vino/vino-server

[Step 5] Mac: Connect via VNC

Press Command+Space keys to open the Spotlight search bar and type the following to connect to your Ubuntu machine:

vnc://<your_ubuntu_address>

[Bonus] Headless Desktop

This link gives a solution for supporting headless desktop.
Personally, I Installed XFCE and changed crypt_level=high to crypt_level=none in the file /etc/xrdp/xrdp.ini as described in this link for improving the responsivness of the remote desktop.