@TVA: Your file is 100% fine, so we need to look elsewhere for the problem.
By the way, because you didn’t name your OS, I suppose that you are using Windows, so don’t wonder about my wording if you use a different OS!
My gut feeling is that your PC has reached its memory limits, because even though the file stored on the HDD is only 122 MB in size, when loaded into Krita it takes up over 2 GB of memory, a size that my PC can easily handle as it was built for graphics processing and has 96 GB of RAM.
Here you will find a folder with your file and my working copy of it (Christmas 2025 - WORKING COPY FOR ME.kra). The folder also contains the files described below, which I created in the hope that you will be able to continue working with them.
I have broken your file down into smaller chunks to hopefully enable you to continue working with it. First, I transferred all currently hidden layers to a new document (Christmas 2025 - unused things swapped out.kra). secondly, I created a “New Layer From Visible” from each of the visible layer groups and transferred them all together into another document (Christmas 2025 - simplified.kra), thirdly, I created a data-reduced but information-identical version (Christmas 2025 - shrinked healthy - NO INFORMATION LOST.kra).
You should, while further editing your file, always flatten your completed groups via “New Layer From Visible” after you disabled the display of all other content. This way, you will be saving used memory space, without changing the look of your document. After flattening, delete the group if the result is okay.
I could imagine that your memory usage indicator in Krita’s status bar at the bottom of the user interface, also known as the “Memory Widget,” was glowing at least yellow, if not red or even deep purple, which is a warning that resources are running low. This is a sample screenshot, but I colored it myself, as I rarely work on such gigantic projects that would force my PC to display such an alarm.
If this was the case, you will probably have to close all applications that are not necessary for painting when editing such large files in the future. For example, browsers, music players, Discord, chat apps, etc., but also all unnecessary mini-applications in the so-called system tray area, usually at the bottom right next to the clock, which often consume a lot of memory.
Michelist