Iguazu borders between Brazil and Argentina
To visit both sides of the falls, one must cross the borders between Argentina and Brazil
If one is at hotels in Argentina and want to visit the iguassu falls in Brazil and vice-versa, it is possible to visit the falls without having a covid negative test. One must to bring only the covid-19 vaccine proof (two doses), they accept a digital one.
If one is in Foz, Brazil and visit the falls in Argentina and return to Brazil on the same day, must to fill in the ddjj form. The same for people that are in Puerto Iguazu, Argentina on the way back after visiting the falls in Brazil.
For people that are in Brazil, entering in Argentina and travel further they ARE NOT requiring a swab antigen negative test OR a 72 hours PCR negative test ANYMORE. One need to fill in this form: https://ddjj.migraciones.gob.ar/app/home.php and show it at the border (it can be a digital on the phone).
If one travel further in Argentina one must have travel insurance.
The system allows people to fill in the form only 48 hours before entering in Argentina.
Government in Brazil is not asking for people to fill in forms anymore to enter in Brazil with passports.
Borders between Brazil and Paraguay
To enter Paraguay and travel further one needs to stamp the passport at the border and show the covide-19 three doses vaccine proof plus also yellow fever card (no need anymore to fill in the healthy declaration)
No need any requirement for children under 12 years old
More information about the requirements to cross the borders and enter in Paraguay: https://www.mspbs.gov.py/portal/22526/requisitos-para-ingresar-a-paraguay.html
For people that visit ONLY Ciudad del Este city, they don't require anything. People usually go to Paraguay for shopping because of the duty-free market.
There is a small waterfall called Monday falls near Puerto Franco town. One can also visit the Itaipu Dam from the Paraguayan side. In the city, there is also a handicraft market with souvenirs.
Note: National Park in Iguassu Brazil closes on Mondays.