The "Sale Goals" feature is primarily a motivational tool designed to encourage community support during sales. To use this feature, you need to create a sale for your game and set a financial goal for that sale. Once the sale is active, the progress bar will automatically appear on your game pages.
If you don't want to run sales but still recieve donations and maybe have a progress bar, you could embed custom widgets or buttons into your game page.
Ko-fi provides widgets you can embed, like a donation button to drive people into your Kofi page, a donation panel that lets people donate directly from the widget or even become a monthly supporter, and of course there's the Kofi goal bar, which displays the live progress on your active Kofi goal. All those can be embeded on the "Description" from you game page.
You could potentially make your own widgets and embed them but that would require more coding knowledge and possibly a backend server, and to be honest I'm not an actual expert on that.