It’s a free country (sorta). If someone wants to spread Russian propaganda they are just as free as those that want to spread Ukraine propaganda or any country really.
Agents of a foreign power must register. Otherwise illegal.
“FARA mandates that you must register before acting as an agent of a foreign principal. Under Section 612(a) of FARA, parties must file a registration statement within 10 days of having agreed to act as an agent of a foreign principal. A party may not begin to act as an agent of a foreign principal before registering.”