While there is legitimate variation in how jurisdictions will treat a public domain dedication (e.g. wrt rights which can be relinquished vs can't be relinquish

While there is legitimate variation in how jurisdictions will treat a public domain dedication (e.g. wrt rights which can be relinquished vs can't be relinquished vs must be explicitly forgone, which a public domain dedication doesn't necessarily achieve), realistically (a) you're pretty unlikely to get sued by someone who tried to dedicate their thing to the public domain (b) the intersection of "jurisdictions that will read a foreign litigant's public domain dedication as All rights reserved" and "jurisdictions whose opinions anyone particularly cares about" is approximately empty.