Inside a particular text file, you can use a modern text editor - (Neo)Vim, Helix, probably others let you to copy/paste via named “registers” (places to store copied stuff). Select something, then "ay to copy into “a”, then "bp to paste from “b”.

I use copyq for this purpose. It doesn’t do exactly what you’ve asked for, but it solves a very similar underlying problem.

I found a solution today using Fcitx, the clipboard addon, and the default shortcut Ctrl+semicolon. However, it works more like a history that pushes each older item down, rather than 10 separately accessible boxes. It seems as though it will work with the use case you described.

Note: I have no idea how well Fcitx is supported in Wayland.

One of the big problems with this is there is no global shortcut for copy and pasting. At most there are the primary, secondary and selection buffers which applications can copy into and paste from. But each application handles the copy/pasting functionality in their own way. Or rather they typically let the toolkit they are using deal with it.

Klipper, the kde clipboard manager comes close to something like what you want. You can CTRL+C multiple times and it stores a history of everything, then you can assign shortcuts to cycle through the entries and paste them out again. All it is really doing is reading the clipboard when it changes, saving that value than essentially copying from that saved list when you cycle though it. So it would be possible to write something similar that has specific numbered buffers - but you would still be saving/loading into the primary clipboard which applications can then paste from rather than creating a new set of shortcuts to paste from each buffer directly into an application.