Thanks for this idea, I thought to try it this way first before potentially considering the regex filter approach.
After reading a tutorial on how-to-use-transformations and then some further research (due to slight changes between OH3 and OH4 as I understand, I could finally make it work. Thanks again so much for the code, it would have taken me quite some time to figure it out on my own.
As you instructed, I registered the code as a transformation in Settings → Transformations. Tranformation Type “JS”.
Saved that and then went to the according thing. Under Channels, I selected the channel and clicked on the linked item.
There I selected “SCRIPT ECMAScript (ECMAScript 262 Edition 11)” which seems to represent the former JS profile name (which was much easier to comprehend 
).
Then select the script in the “thing to item transformation” and good-to-go 
P.S: I had to alter the code slightly. The if clause needs to trigger true for the last value being null. I therefore changed to check the cache.private.get(‘last’) directly. parseFloat apparently returns a NaN if the input value is null, therefore the if check didn’t trigger.
(function(data) {
const THRESHOLD = 50;
const lastValue = parseFloat(cache.private.get('last'));
const currValue = parseFloat(data);
if(cache.private.get('last') === null
|| Math.abs(currValue - lastValue) >= THRESHOLD) {
cache.private.put('last', currValue);
return data;
}
return cache.private.get('last');
})(input)