Armbian has sane defaults for SBCs as well (yes log2ram so you won’t burn SD cards) and it is way more stable and polished than DietPi with less overhead. About bare Debian, you’ve the images I linked to and you can make it log to the ram with a simple line in systemd’s config.
Storage= Controls where to store journal data. One of “volatile” (…) If “volatile”, journal log data will be stored only in memory, i.e. below the /run/log/journal hierarchy (which is created if needed).