You can save the user profile picture as an ico icon. (Patreon)

New feature in version 6.8.0: You can save the user profile picture as an ico icon.

In the user page or the work page, click the "Other" tab of the download panel to see this button.

After clicking, the downloader will save the user's avatar as an ico file of 256*256 pixels. The ico file can be set as a folder icon, so you can set the icon of the artist folder as the pixiv profile picture of the artist.