sorry i can not comment on that error you have,
but sure:
i run Processing 3.4 on Raspberry Pi what has only
- 1GB LPDDR2 SDRAM ( and that shared with GPU )
and on OS RASPBIAN
DEBIAN stretch
Linux version 4.14.79-v7+
so the RAM is not the problem.
but pls tell us more about what you did?
- is it first installation debian
- first install processing / first start attempt?
- or was it running and you installed any library?
as you point out that you use DEBIAN “sid”
so what rev you have actually installed?
possibly a other user here uses it too?