How to use FanGrowth in an incognito window
Step 1:
Install FanGrowth from Chrome Store in your normal, non-incognito window. Here's the link.
Step 2:
Go to this url in your browser: chrome://extensions
Step 3:
Click on Details button on the FanGrowth extension card:

Step 4:
Scroll down to the "Allow in Incognito" toggle. Turn it on:

That's all! You can now go back to fansly.com on your incognito browser.