I might have suspected lack of swap being the culprit, but from your system information it seems at least sufficient.
Aside:- Adding zram at a future time may enhance performance to some extent (See: Add a backing SWAP device to zram (and enable hibernation)); but this is unrelated.
Another potential culprit is lack of available space. Usage seems fair at ~30% overall, but temporary files generated by graphic applications can at times be excessive.
A quick Internet search revealed the crashes you describe have been reported for several years, without any definitive solution. One suggestion I found was to avoid saving to removable USB media; or any non-pool volume on other disks; this doesn’t seem applicable in your case.
You might consider checking the destination file system for consistency. I’m not familiar enough with BTRFS to make any recommendations regarding appropriate tools to use.
And then, there is this:
- Crash on Export as PNG in PNG Dialog (GitLab)
Although the issue is three years old, and in a Windows environment, the similarity is obvious. This might be indicative of a bug in Inkscape that has prevailed for some time.
There was also a note about GIO (the GtkFileChooser).
I interpreted that as suggesting the cause of the crash might have been attributed to the save dialog as opposed Inkscape itself.
Unfortunately, all this equates to a huge 
on my part. You might take some consolation from the fact that you’re apparently not alone:
- Export to PNG Freezes Inkscape
- Inkscape 1.1 is closing when trying to export images
- Crash when export to PNG image
- Inkscape freezes and crashes during export of large projects
There appears to be nothing specifically pointing to Manjaro (or Arch-based distributions) as being a contributor. However, allow time for others to respond in case anything else comes to light.
Otherwise, I’d suggest opening a new issue upstream:
- Inkscape (Gitlab)
Cheers.