Donations hasn’t been a successful path for the wider internet, no reason to expect any difference here. Ads embedded in the images, or perhaps listen to a message from our sponsor while we prepare your PDF?
Works pretty well for Wikimedia which has gotten incredibly rich while providing an essential service for the internet public. (Off the back of volunteers, of course.)
Donations likely won't work, but a combination of realistic publishing fees that do not enrich a publishing house plus government sponsorship (which would sort of happen implicitly when those fees are paid from grant money) likely would.
Even just the basic admin costs associated with paper review - handling that for a medium sized journal is at least one full time job - are going to add up to more than I think donations will ever generate for such a task.
My mental model is a non-print journal, so there are very few "publishing" costs, but the overall administration of things, from the tech side to the typical scientific paper processing workflow, is not a long term task for volunteers (I suspect).