Mlem dev here. You can attach a link to the post directly by clicking the link button in the post editor toolbar then tapping “Paste” (with a link copied to clipboard). We’re aware that this isn’t the most obvious UI, and are improving the design in the next version.
On Mlem you can add a link by tapping the link icon at the top of the post editor and tapping “paste” (with the link copied to clipboard, of course). We’re aware that this isn’t the most obvious UI, and are improving it in the next version.