In macOS 14 Sonoma, Apple introduced some updates in Safari, including the "Add to Dock command".

Now, you can easily convert the necessary website into a standalone app just within a click.

To do so, go to "File" menu in Safari menu bar and click "Add to Dock".
On the window that has just appeared, type in the name for your app.

After clicking "Add", the icon of the new app will appear.

Now, you are having a standalone app based on a existing website!