1. Are there images in note?
2. Big amount of images?
3. Large images?
4. Or only hand writing?
5. Do you synchronize to nextcloud?

Only handwriting, and ~ 25 pages (@QubaB Sorry, previously I mistakenly opened another note and the number of pages is now corrected, although I have not tested systematically whether this could happen for documents with fewer pages). Synchronize to the official server.

I observe lag during autosave (created testing note with 10 pages of handwriting).

I do not know if this can be avoided. I do not understand source code enough to see if saving is done in another thread (on background) or whole Saber runs in only one thread and then saving should produce lags.

I think that lag is caused by creation of note thumbnail during each Save. When I turned off creation of thumbnails (in developer version), lagging was not almost noticable.

I will try to create fix, which will implement that during autosave is not created thumbnail.

I do not understand source code enough to see if saving is done in another thread (on background) or whole Saber runs in only one thread and then saving should produce lags.

It is done in background: #179 (comment)

I think that lag is caused by creation of note thumbnail during each Save.

I guess that thumbernails should be produced when the notes are closed. Doing it during autosaves does not seem to be meaningful, indeed.

I experienced a lot of lags too, with Appimage v0.21.4, even on short notes (3 pages, but with a few emoji images).

I was also experiencing lags during autosave. I have disabled autosave and just make sure I save before I exit. Dramatically improved the usage of the app.

I haven't done an exhaustive search, but 0.21.0 seems to not have this issue. I reckon it's caused by a95f44b, which makes it a duplicate of #1189. Autosaving causes roughly the same amount of lag as simply saving to exit.