Thank you for the context. I was an Affinity Suite user for a long time after I dropped Adobe.
I now use a mixture of GIMP, Krita, and Inkscape for visual things. I don't have a good alternative for InDesign - even Affinity Publisher wasn't one. Since my tabletop RPG business closed, I haven't had a need for a powerful layout application. I just use Typst or LaTeX for my personal projects that need a layout engine.
It doesn't come close to InDesign, but for some purposes Scribus [1] might be a viable alternative. I use it (in combination with a lot of Python scripting) to produce a printed diary every year.
There really is none, at least not that is comparable. InDesign is perhaps the one product where Adobe really shines.
Aldus PageMaker and Quark XPress were worthy predecessors; I used both back in the day, but Adobe bought PageMaker and discontinued it. As for Quark, not sure what happened to them but they're not around anymore.
I used Quark XPress, and it really felt like it had a monopoly on the professional market in the UK at the time. It didn't really innovate, it was slow and clunky. Then InDesign came along and it was a breath of fresh air.
Took many years for the transition to happen, but a lot of people in my circle wanted to see the back of Quark.
When I worked in desktop publishing (35 years ago, sigh) we used Ready, Set, Go extensively. Certainly seemed like a more intuitive UI than what little I've seen of Quark, at least.
After using InDesign CS6 for many years, (small-scale print/publishing), and trying Affinity Publisher for a time, I stumbled across VivaDesigner a while ago: https://viva.systems/designer/
I don't know how it compares to QuarkXpress, but it's a pretty good commercial replacement for InDesign / Publisher in my personal opinion: it has decent typography, styles, and good options for PDF/X-4 export (with FOGRA39 as a destination etc). I've also successfully imported .idml
They have various perpetual / subscription options (I'm on a commercial perpetual licence), a decent trial version, and they even do a Linux version, which works great for me on Mageia9.
I've contacted their support a few times, and they've been very responsive, professional and helpful, which was a pleasant surprise.
I now use a mixture of GIMP, Krita, and Inkscape for visual things. I don't have a good alternative for InDesign - even Affinity Publisher wasn't one. Since my tabletop RPG business closed, I haven't had a need for a powerful layout application. I just use Typst or LaTeX for my personal projects that need a layout engine.