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.
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[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?
The biggest game changers towards the end of the war we're strategic rather than tactical. Namely the economic dominance of the Entente and the crippling blockade of the Central powers. This enabled the Allies to weather the effects of the huge manpower losses in the earlier years of the war.
As far as tactics go, the biggest shift was to move away from the massed infantry assault (big artillery bombardment followed by a massed infantry charge towards the enemy line) and moving more towards infiltration where smaller groups of soldiers would sneak across no man's land and attack specific installations before the rest of the infantry, now supported by tanks, would attack en masse.