I saw that these Passenger locator forms were required, but now I can't find the form or why it is needed. Is this Covid related? what agency is asking for the form? Are they still being required? We travel in June on the Best of Europe tour.
I think it depends on the country.
The "agency" is the country you are entering. There is no europe-wide form so you will need to look at each country. Additionally, some might only require it for air arrivals, not land. Just depends. If you are on the tour, the guide will know, so you might just need to check on the country you arrive into before the tour (including any layovers) and any countries you enter after the tour, independently.
I know that several countries have removed the requirement for these forms, but as it is country by country, I'm sure some still have them.
We are flying United to France at the end of June. In the "Travel Ready" section it lists the EU PLF as a required form (there is a link to the form). United Airlines states "We don’t need to verify your documents, but government officials may inspect them". I printed out the completed form and will have it if needed. It was simple to fill out.