is there some way to Merge down basic layers?

[ldd2]

Hey hello. I've been using gimp 2.10.2 for a very long time. Just recently now updated to 3.0.2.

When used to work with older version, I used to paste lots of sub-images into the main one, to then right click in any empty space from main image to keep modifying pixels or adding up more sub-images, but here in v3.0.2 after pasting first sub-image, I get some small black lines which indicate to be the limit from new recently made "layer".

In v2.10.2 I didn't use to have this problem. Its not like there were made new "layers" when posting new pixels or sub-images to main image. I know there is a command named as "Merge down", but would like to know if there is some option to keep the same old behavior I used to have in older GIMP version.
It would be tedious to be pressed Merge down each time to add up a new sub-image to each one of the files that have to modify.

Dont know if its called other way around to make it automatic, so sorry about ignorance and thanks a lot in advance.

[Ofnuts]

You can use Edit > Paste as floating data (and perhaps reset the Ctrl-V shortcut to it) to get the old behavior.

In modern Gimp, the floating selection is generally considered a nuisance, it was a cop-out when RAM was scarce. Now you mostly keep your layers distinct, merging is easy, separating is often near impossible.