Do you or have you considered having your members an option to Donate?
I can understand not wanting to switch to something like Discord as it is more of an Online chat than a messaging board. Plus with Discourse Chat plugin not a lot of need for a Discord server.
As mentioned tge Ad plugin can be a good fit. There is also the Amazon Affliates plugin. You would likely need to rebake posts to have ir adjust older posts with Amazon links.
Chat plugin could even for example be offered as a ViP option for users whom donate say something like $20/year along with other perks. Humble bundles for example you could give a free game code every say 3 ir 4 months. Just purchase a few packages…