patreon's tos or itch's tos?
because, well, look at your itch settings, misc, connected accounts...
Linking to your patreon is not a problem. Do it on your profile, on your game, wherever you want.
But there might be problems in some cases for the content offered. Some dev claimed that they cannot offer the same version that is beyond a patreon paywall elsewhere. (Or was it patched/full versions? Can't remember exactly what was the problem. Point is, itch even lets you integrate patreon, whyever would anyone think that linking to patreon was forbidden.)