The point taken and well deserved. 
My only consolation is that I’m not the only one in this forum “guilty” of switching and trying apps too often. But, I’m working on breaking what in excess is an unproductive habit.
I’m pretty settled at this point. 
I’ve tried everything and I believe I’ve found the right combination of apps that do what I need while keeping subscriptions to a minimum.
I’ve come to realize that it is “ok” to use rich text based applications. I never questioned this before joining this forum but I got swept up on the plain text bandwagon.
Having resolved this matter in my mind, I quickly concluded that Scrivener for large projects like books is superior to other options. I also discovered that it was user error and not Scrivener that caused the syncing problem I mentioned in this post. Scrivener tech support pointed out my error. Scrivener is working and syncing flawlessly.
Moreover, while I’m now more comfortable using a rich text based application like Scrivener, I still value the portability and future proofing of plain text files. Once I understood that I could export/compile rich text from Scrivener to markdown and that I could bulk export to markdown from Ulysses, I realized I was making this way too hard and that the Ulysses subscription was well worth it for short to medium length projects. And, I can always bulk convert files using DEVONthink.
At this point I only have four app subscriptions and they are serving me well: Ulysses, 1Password, MindNode, and Bookends. As I’ve noted, probably ad nauseam to some in this forum–for which I apologize, I have moved to Apple’s native apps for mail, notes, calendaring and tasks. I have DEVONthink primarily as a powerful file conversion and OCR utility. I’m using Scrivener and Ulysses for writing and Obsidian for research notes.
My doc reflects my app choices.
So, I admit that I’ve been a bit (a lot?) all over the place but I’m confident that there will be little need for significant changes in app choices and workflow going forward.
