I don't know that any book is better than web resources, now, as long as you can spot and avoid the AI that is infesting the web. And don't overlook real life.

I don't know what sort of resources you might have locally. In MT we have an amazing NFP network. Locally, they hold brown bag lunch sessions. One of the things I tell my QB students is to go volunteer somewhere, because they will not get a better experience than to see NFP finances from the ground, up. Example:

https://www.mtnonprofit.org/tax-season-for-nonprofits-3-things-you-need-to-know/

Your advantage is that you get to reference their prior year filings, too. Working with local agencies allows you to see the differences in fund accounting, learn how to handle group exemptions, how reporting to a parent organization is done.

Lastly, if you have a United Way, I recommend offering your time to them. OMG, I cannot even begin to tell you how much I learned from their review process, because they have a fine edge and developed great methodology that you get to see applied to a larger number of NFP entities in one cycle than you might run into in 5 years of preparing 990 forms.

And I'm just a huge advocate for volunteering.