Side bar on the main page, under "donations". I'm posting a screenshot instead of a donation link so you know I'm not scamming... Plus there's multiple ways to donate.

Edit: the target accounts/links I looked at a few weeks ago are under "mastodon.world" but go to the same place. There's an explanation of why but I forget which page I read it on

Edit X2: the explanation is on the patreon blog post : https://www.patreon.com/posts/welcome-lemmy-84892927