@ofnuts "Why are you using Legacy?"
Short answer: Because I find Legacy effects predictable. (And because I've never taken time to understand the difference.)
Longer answer: When my workflow became unpredictable because of an upgrade, I posted what had happened and was informed that I could get back to what I was used to by making the Layers Legacy. [...which meant doing odd things with 8-bit GIMP to get clever results which 32-bit GIMP can likely now do straightforwardly]
As I recall, the motivation was a problem in this very area of "stacking layers" to get certain effects.
Like all habits, and I don't know if this one is bad
per se, it is almost automatic for me to Create a Layer and Make it Legacy. And like some other old people who come to mind, I tend to prefer sticking to old habits to spending unknown amounts of time learning something new. (I hasten to add that I have often paid dearly for that one too: wasting more time avoiding learning than it would have taken to learn it. On the flip side, I have also beaten my head against a wall--C++--to learn something that remained just outside my grasp than it would have taken to just do it the way I knew. That I suspect is a common trait.)
[I just checked and found that there's no discernible difference between the modes on the stacking-for-blending I'm trying to do. At your instigation, I'll spend some of my precious time to look into the differences to give a bettter answer, or just drop the habit. Counting up the second or two it takes me to enable Legacy, I've probably got a couple of years invested in that practice.]
[Update: on my very first search for "Legacy Default difference" I found
this "smoking gun".
]
[And wouldn't you know, pasting the weblink in here, I found the user interface for "Web address" quite different from what I'm used to from other sites. Another choice: investigate how GimpChat wants me to format it, or paste it raw "because the probability I'll need to do it again--a lot--is low?"]
[Update: I found the circled question mark icon to the upper right, taking me directly to the formatting guide, so I'm fixing the weblinks.]
[Update: I posted results of my very second search to
this new topic, showing off my now compleat mastery of Web Address.]
Cheers!