By the sound of it, whiteboards are not yet safe if you can’t afford to lose the work. For what it’s worth, I’ve spent about three weeks using a whiteboard to plan projects for a modded Minecraft server, and haven’t lost anything yet. If you want to use excalidraw as suggested by @jkmontoro, but stay with Logseq, you can use either the built in Excalidraw integration or the Excalidraw plugin for Logseq. In my opinion, the plugin is better. It fullscreens the canvas while you draw, and then neatly hides the controls when displaying as an inline image. Less cluttery than the always-visible controls on the regular Excalidraw integration.