I'm new here from Reddit. I was a former Digg user. Over the past few years, Reddit has gotten swamped with spam and low quality content. I was most at home there on the niche subreddits that were still earnest and not spammy. I hope things stay that way over here.
I've made a small donation to help Lemmy grow. It's not much, but scaling up to handle the escapees is a big deal. Having the money to grow and build robust processes to keep content thoughtful and helpful is important. While I love the funny posts and memes sometimes on reddit, it's really infested the popular subreddits to the point of being excessive. Ergo, I tend to hang out in smaller spaces where the dialog is more "straight up".
I found it on the main lemmy page where you sign up for a server. It probably needs to be posted in more places, like on the communities pages. (there's a patreon site too where you can donate)
Here is their donation page with all three currently supported options.
I don't know much about Open Collective, but LiberaPay does not take a cut (only the fees of the payment processors) so I would discourage you to choose Patreon.
Edit: Actually there are more options listed since you can also donate crypto.