On another (64 bit) linux computer I am able to mount the volume without any problem. Can the error message have something to do with the Turris Omnia hardware still being 32-bit? If I search the internet for this error message, I find a lot of references mentioning the 32-bit to 64 bit difference.
The 32-bit hardware is also the reason why the Nextcloud version officially provided with Turris OS is still version 24 (24.0.9-5), while the lastest Nextcloud is version 30. See: Future of Nextcloud in Turris OS