This thread asks for larger thumbnails in image baskets, so grubbed a bit w/o luck, sorry.

But I found a registry key, that allows to open more than five baskets:
Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\ACD Systems\ACDSee Professional\130\Image Basket Group]
This one sets the maximum number of baskets to 16 for AC Pro 2020. Here's a screen shot:
Click image for larger version  Name:	Screenshot.jpg Views:	0 Size:	82.5 KB ID:	52228
What ever you may do with this gimmick, you use it on your own risk. It might have downsides currently unknown to me.