I recently got a book for what-if fans -

Disaster at D-Day: The Germans Defeat the Allies, June 1944
by Peter Tsouras

https://www.amazon.com/dp/B01G51Q0PQ/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1

Looks like one can do the Kindle for $2.99 or
get the hardcover delivered for $6.79.

"The editor of Hitler Triumphant combines history and fiction to craft
an alternative history of the Normandy landings on D-Day.

It is June, 1944. The Allied armies are poised for the full-scale
invasion of Fortress Europe. Across the Channel, the vaunted Wehrmacht
lies waiting for the signs of invasion, ready for the final battle . . .

What happens next is well-known to any student of modern history. The
outcome could easily have been very different, as Peter Tsouras shows in
this masterful and devastating account in which plans, missions, and
landings go horribly wrong.

Tsouras firmly bases his narrative on facts but introduces minor
adjustments at the opening of the campaign—the repositioning of a unit,
bad weather and misjudged orders—and examines their effect as they
gather momentum and impact on all subsequent events. Without deviating
from the genuine possibilities of the situation, he presents a scenario
that keeps the reader guessing and changes the course of history.

Praise for Disaster at D-Day

“A brilliant and interesting book. The author has pulled off a great
feat of imagination and research.” —Military Illustrated

“This should find a place on the shelves of anyone with an interest in
the period and would be invaluable background reading in preparation for
a battlefield tour of Normandy.” —The British Army Review"

one review is
"Change a couple of factors and Operation Overlord ends in a failure for
the Allies. Few people realize just how close the operation actually
was. The changes were not major, but quickly snowballed as Dame Luck
came into play. A disasterous situation at Omaha Beach closes that area
off. The capture of an Allied secret map convinces Hitler that this is
the main thrust and frees up the reserves at Pas de Calais for defense.
Had this happened, it would have been a true disaster from the British,
who were already scraping the bottom of the manpower barrel. Good
alternate history is interesting. This one is fascinating. The only nit
to pick is that it's VERY detailed and that occasionally bogs down the
story, but it's pretty much a minor point."

another
"Like most other reviewers I give this book four stars. Most of it I
liked, a couple of points I didn't.

The good points: First, and most important is how a relatively
few,relatively minor changes might have indeed reversed the outcome. In
reality Rommel had only one Panzer division near the beach, in the book
Hitler had allowed him to move another division into the area. Second,
von Rundstedt is able to convince Hitler that this is the real invasion
and get the release of many more divisions to be sent to Normandy. In
reality the Germans held these divisions elsewhere until too late.
Third, and the final one I'll mention is that the guns at Pointe-du-Hoc
were installed with their supporting forces and the Rangers didn't quite
make it to the top because of the additional troops up there.

There are other good points as well, but there's no point in telling the
whole story in a short review. If you want to know, read the book.

Let's get the bad out of the way. First, it is written like a lot of
military history: The US 18th Armored was here doing this. The British
24th Infantry was there doing that. The 29th SS Panzer was somewhere
else doing something else. It even has fictional references to books
published after the war on the actions of these divisions. As such, I
sometimes had problems keeping the overall picture in mind (as I do with
some real history). The story doesn't come through as easily as some
other approaches such as that which Turtledove uses. Second, this
shouldn't be the first book you read on D-Day. If so, you might never
understand what really happened. Third, he repeats the claims made by
Montgomery after the war that the battle turned out just the way he had
planned it in advance. Actually, the author quotes this point from one
of his fictional references, but finding this requires a pretty close
reading.

The biggest overall thing that I brought away from the book is
realizing, like Wellington talking about Waterloo, that the D-Day
invasion was "a very nearly run thing." It could indeed have gone the
other way."

or, one can also read what the readers at Goodreads write:
(Their rating is only 3.73!)
https://www.goodreads.com/book/show/1619710.Disaster_at_D_Day