Do I need a negative PCR test PER country?

I traveled last month through 3 countries and have planned trip coming up in the Fall 2021.
Given how things change during the pandemic with variant outbreaks I would wait until April 2022 before asking or researching what the requirements would be for entering different countries for a trip in June 2022. There is no way anyway here could give you the facts you need to know for a trip that far in advance. Hopefully things will be favorable by then.
Use only official government websites only to get facts about requirements. For example the US State department website has travel information on most countries
https://travel.state.gov/content/travel/en/international-travel/International-Travel-Country-Information-Pages.html

Jazz is dead right. At this point, just know that you'll need to check on the requirements (which may turn out to be nil) for every border crossing. There may be better online resources for doing that research by next spring than exist today.

You need to look at the government websites for each country that you are proposing to visit, but these provisions are likely to change numerous times before next June.

A trip this year covering so many countries would have been fraught with difficulties due travel being restricted, testing and quarantine. This summer, there has been a 5 day quarantine on arriving in Italy from the U.K., France banned people going there from the U.K. etc. Is the Covid situation going to be much better next year? No one knows, but Covid isn’t going to disappear.

Countries amend their policies with around 48 hours notice, so your plans may have to change mid trip. I would consider either booking your trip much closer to June than January or simplifying your itinerary to say one or two countries. Ensure everything is flexible or refundable.

It is impossible to know this for a trip in June 2022.

nobody knows yet.

You need to check much much closer to your travel time. Thinks could get tighter or looser, and that can vary on every boundary.

Most required tests are not PCR which are expensive and relatively slow - many accept one or more of the quicker and cheaper antigen or Lateral Flow tests.....

You won't know until months from now what the situation with contagion is at the time and the current requirements...

While I agree with the other posters that it too early to come up with a definitive answer, there are some basics that you need to know to facilitate planning.

This website is handy in that it presents a single source of high quality information: https://www.iatatravelcentre.com/ it has a handy map that you can click on the country, and see what measures are in place. It is then a good idea to then find the official site for the country to verify data. As an example, this one is for Italy: https://www.salute.gov.it/portale/nuovocoronavirus/dettaglioContenutiNuovoCoronavirus.jsp?lingua=english&id=5412&area=nuovoCoronavirus&menu=vuoto

Keep in mind, that countries mainly look at where you are coming from, not your nationality, and where you have been in the last 14 days, so by the time you enter your fourth country, you need to consider any measure for maybe 3 or 4 countries you recently were in. In regard to nationality, some rules can be different, in that legal residents of that country do have some exceptions, and in the EU, residents of other EU countries may have some rights that you do not as a non-resident.

There are some provisions for travelers who may just cross the border for a few hours to a day, but generally, if you stay overnight, you need to fulfill any requirements. Even for one night, if testing is required, you likely will have to test, or at least are obligated. If the rule is something like "test within 3 days of arrival" and you are just staying overnight, I guess you can reason you left before the requirement kicked in.

Do also remember that there are usually one set of rules for entry, then another set of rules for day to day life. So while a test might be needed for entry, further tests might be needed for specific activities, or proof of vaccination.

Hopefully by June 2022, all this will just be a bad memory.

Next June? I leave in six weeks and I'm not even going to see what is necessary until the middle of this month. Rules are consetantly changing.

As others have stated, it's impossible to know what the rules will be that far in the future. As for websites, this forum has been pretty good with keeping people up to date.

Thank you for the responses and a special thanks to those who shared those links.

I know it seems premature, but I don’t want to start booking stuff only a month in advance and I certainly don’t want to wait to find out my 5 country trip can now only be a 1 country trip...only a few weeks before said trip. I don’t want to sound like a defeatist, but it would seriously kill most of the excitement about my trip RIGHT before said trip. I would seriously rather not go than have that happen. Plus I can’t afford to fly back and forth to Europe doing only 1-2 countries at a time.

I’m just venting though hahaha. Obviously no one here has any control of anything. But hey, thanks for the advice and links. I appreciate everybody’s time :)

I'm not sure exactly how many days you have available, but I can assure you that every one of the countries you list can easily fill two months or more--though I acknowledge than two months in Switzerland would cost a pretty penny. Within any of those countries you have a great variety of scenery, culture, sights and often also language and food. You don't need to cross so many (or any) borders! France is much, much more than Paris; Italy is much, much more than Venice, Florence and Rome.

"If the rule is something like "test within 3 days of arrival" and you are just staying overnight, I guess you can reason you left before the requirement kicked in." Doesn't this mean you have to be tested within the 3 days BEFORE you arrive in a country and you MUST test negative? I leave soon for Croatia, then entering Italy (Sicily, then Milan area), then a flight to Frankfurt Airport in Germany, then a connecting flight to Newark, NJ, USA. I might need 3 tests: Italy, maybe Frankfurt, then USA. Should be be sure to buy tests and pack in my carry-on?