My understanding of WW1 had always been that its style of trench warfare was stable throughout the entire war. That is to say, the only defense against the new weaponry was to dig trenches, and the only way to capture trenches was to throw a few thousand men at them, at which point, you may have gained a few hundred yards. This continued until Germany ran out of resources.
What ultimately moved us past trench warfare, the story goes, was the improvement of the tank.
But a few years ago, I listened to a podcast (which may as well have been called Testosterone Drenched History, the actual name escapes me) that claimed that tactics had been updated near the end of the war; the war was becoming more mobile, ground was being transferred more quickly. It did not get into details.
I stumbled across this webpage (https://www.warhistoryonline.com/world-war-i/breaking-the-deadlock-machine-gun.html) that credits light machine gun units (with ample supplies of grenades) for breaking the stalemate.
And a piefed user supplied this somewhat cryptic (to someone who doesn´t read ~~German~~ Norweigan) diagram of how to take out a machine gun nest.
\
[translation provided in comments: suppressive fire and toss in a grenade, repeat]
What is the true story of the tactical situation at the end of WW1?
That diagram is probably cryptic to someone who reads German as well, as it is in Norwegian. Not that I have any knowledge to what you're asking in the first place.