The project size exceeds the available free space on the target disk

At first I got this error because my notebook only had 50GB of space left and the project I recorded was already taking 26GB of space in /var/tmp … So I ordered a high-performance 512GB SD card to expand the available storage. It’s formatted in Ext4 btw. But I still get the same error message when trying to save to that SD card. How is that possible?
After copying a couple of files from my internal SSD to the SD card (until i had about 40GB of space left again) I was still not able to save the project to the SD card. I was however able to save it to the SSD then and finally copy it to the SD card.

I would really like to be able to save my projects to the 500GB SD card directly in the future. It worries me that audacity it having issues with that. I’m not even sure if I’ll be able to open and save that project without going through this whole workaround again. Any ideas?

Audacity version: 3.2.1

Windows guy here. Can you post a screenshot of the error message ?