FTP and Training Readiness!

When you get a new lactic threshold running result on the watch, it will display the threshold power you were running at. That is pretty much the running equivalent of the cycling FTP. Strangely enough, you will not find this metric stored. It will only store the threshold heart rate and pace.

Ok, but in every other place Garmin has a clear distinction between LT(running) and FTP(cycling):
https://www.garmin.com/en-US/garmin-technology/running-science/physiological-measurements/lactate-threshold/
https://www.garmin.com/en-US/garmin-technology/cycling-science/physiological-measurements/ftp/
Even on the store page of the 255 you can find 2 separate entries, one for the LT functionality and one for the FTP functionality:

So it is absolutely certain that FTP refers only to cycling FTP, not to running LT. And so it is absolutely certain that Garmin is lying about that feature being on the 255 even after we notified them about it being wrong.

Guys, I use my fr255 for running/gym, I've just once tried 1km of bike and I have some FTP values under: other/performance statistics/power threshold. Here I have ftp for cycling and skiing.

What is missing is the possibility to run a test like the LT test with a chest strap for running or what?

FTP functionality refers to FTP autodetection and the FTP test (both with a cheststrap and a powermeter). Both are missing from the 255. You can verify this because there is no option to activate the FTP autodetection and there is no option to perform a FTP test. A watch that supports those features, like the 955, has those options in the menus. Plus Garmin itself removed the information on the feature from the 255 manual, confirming again that the feature is not present in the 255.

What you are talking about, from the way you described the menus, is the power threshold page in Garmin Connect. That page contains data for every device you have ever had, so those numbers you are seeing probably come from another device (or see below). You also say that your supposed FTP estimate came from a 1km cycling activity, but according to the 955 manual, even if the 255 had a FTP autodetection function (which it doesn't), you would have to record a steady, high intensity ride, and a 1km test bike ride doesn't fit that (information on the test from here).

It could also be that those numbers are the result of a bug of Garmin Connect which makes values appear out of thin air in the power threshold page, like you are describing: Ghost ftp for cross-country skiing? Never ever started an activity!.
But that problem is to be discussed on his own thread, here we already have confirmed that the 255 is missing the features and that those exact features are being falsely advertised (see previous posts).