ads678, do you know the old M-ETA system? It’s not a travel reducer, it is an rebound speed adjuster that traps the fork when compressed down to about 30mm of it’s previous length, which in turn drops the front end height and makes the bike much easier to climb steep stuff on, as the front has less tendency to lift or wander.
It was a fantastic system and one i miss too. To the OP; there are travel adjust forks that enable you to adjust travel and front end height on the fly, but only relatively small amouts, eg: 80-100-120, and nothing I’m aware of like eta. Others allow you to lock out, but usually by doing it the opposite way, putting the fork at full extension instead of full compression. Prevents bobbing, but doesn’t lower the front.
Then there are over engineered concepts like dual circuit systems where you can adjust the fore-aft pressures between front and rear shocks to make the rear harder and the front lower – not sure exactly how they do it, google Bionicon if you want.
Last point – if you’ve been away a long time, the shape of bikes in general has changed and to my opinion climb far better now than their predecessors from the time when ETA was around and useful. You might not need it…..