OP didn't mention PoD being a factor, and they mentioned money being a problem. That's why I mentioned Scribus instead of Affinity.
Why did DMsGuild stopped accepting pdfs made with Scribus?
OP didn't mention PoD being a factor, true. But if they ever want to do PoD through DrivethruRPG, they can either use Scribus to create the web PDF and a different program to create the print PDF, or they can choose a different program and just use it for everything.
This page specifies that DTRPG wants the files created in Affinity or Indesign. Note that this is a DrivethruRPG page, so it is not specific to DMSGuild, but anything on DMSGuild will also have to follow these guidelines.
https://help.drivethrupartners.com/...00178583-Quick-Specifications-for-Print-Books
It gets even more fun. Now, it seems that in order to be approved for Print on Demand on DMSGuild, they require you to work with a select list of "Layout Designers," detailed here:
https://help.dmsguild.com/hc/en-us/...ments-Guidelines#h_01HXW5JDT7H85NM0R4T97G8D3Y
I don't remember when they specifically said they no longer accepted files created using Scribus; I can't find the announcement anywhere. It would have been in mid to late 2021 or maybe early 2022, though, shortly after my Zakhara campaign guide was published.
Again, if the OP either isn't ever going to want to do a book as PoD, at least through DrivethruRPG, none of this will matter. For example, I've had books printed on Lulu that I made using Microsoft Word(!).
But if they ARE considering PoD and want to use Drivethru, Scribus is just not a great option.