Looking for updated experience for Venice, multiday transport pass Veniziaunica

If all you want is a 72 hour pass for ACTV vaporettos, then just buy the pass on arrival. I believe there is an ACTV booth at Marco Polo, or buy it at any ACTV booth in Venice.
If you buy the pass on line, you get a voucher that has to be taken to a booth and exchanged for the pass.

The 72 hour validity starts when you first use the pass. You MUST swipe the pass across the reader EVERY time you use it.

is that available for purchase at time of arrival

At the arrival you can hand 'em a voucher, a credit card or some cash. They will give you always the same ACTV pass, but with a voucher you won't need to explain what you want.

But, I can't find prices for a 3 day pass that would be equivalent to what I'm seeing on the tourism site

https://actv.avmspa.it/en/content/venice-urban-services-0 scroll down till the "DAILY AND MULTI-DAY TICKETS" section. 45 € , 3 days.

Confirming Dario's post: In mid-September I stopped at the tourist office in the Venice train station and bought a 168-hour vaporetto pass. My travelmate purchased more--I think it was a sightseeing + vaporetto pass. I wasn't doing the Doge's Palace or the Correr Museum, so the sightseeing pass didn't look like a winner for me.

I also bought the Chorus Pass, a very low-cost pass covering entry to over a dozen churches--though not the really major ones like San Marco. I only broke even on that because I spent a great deal of time looking at glass and just wandering around the city, so I only managed to see four of the churches. I think it's hard to make the Chorus Pass pay off unless you're in Venice for a very long time; I was there nine days. But the Chorus Pass is very inexpensive (and good for a year), so there's no risk of wasting a lot of money on it.

There are some minor vaporetto stops in Venice that have no ticket booth or ticket-vending machine, so be careful about wandering around the city with no ticket or pass in hand. You could end up at an unserviced vaporetto stop and have to wander off to a busier one.

There's been a lot of discussion here about the crowds on the vaporettos and I want to chime in with an observation. We were in Venice for 5 days this past October. The vaporettos were jam-packed - standing room only, shoulder to shoulder with people.

We had a room overlooking two stops right on the Grand Canal and one of the activities we took part in was looking out the window and loudly exclaiming about how many people were on each vaporetto that went by. Early morning, mid-afternoon, late at night - they were always packed.

I like the vaporettos and have purchased the unlimited pass on previous trips but I did not for this past trip as I had read so many notes about the crowding. In the end, it was the right call for us - we did n to use the vaporettos at all and just did more walking.

Thank you all for the great info. Dario, thanks for the link on the prices, so it looks like it would be a savings of 5euro/pass if we got them online at least 30 days in advance. I'm not sure it's worth it although I guess as you mention, they will know exactly what I'm asking for.
Acraven thanks for the info on the chorus pass, very good to know. I don't think we'll get that because we're only there 3 days. I'm curious when you were there in Mid September, did you also see the types of crowds that Valerie witnessed in October?
I have heard that crowds in Italy in 2022 were higher than prepandemic (and that's without Chinese and Russian tourists who in general weren't traveling in 2022.) I am hoping that in late March it will be better although I'm guessing just marginally so.
As for the additional discounts/packages I'll need to do more research to see if it will be worth it to us. With only 3 days, we may not get to too many attractions beyond the Doge's Palace.

I'd been reading about the situation in Italy before my trip--though I think most of the comments were about Rome, so I feared the worst. The vaporetti were generally very crowded. An employee hops off the boat as it pulls into the dock and monitors folks getting off and on, so there was no danger of being absolutely crushed to death. As of September masks were required, and that person also reminded folks who forgot to put on their masks of the rule. I don't know how many vaporetto rides I took over the course of nine days--perhaps about ten. I think I sat down once, maybe twice. I'm 71, and a few people offered me their seat on crowded boats, but I didn't need to usurp someone else's seat.

I encountered a long line at San Marco; it took 30 minutes to get inside. You can buy a low-cost entry ticket online to avoid that wait, and I suspect you don't need to buy that ticket terribly far in advance; trying to buy on the day of visit wasn't working in September. I observed a much shorter line at the Guggenheim Collection--possibly people with tickets waiting for their entry time; I do recommend buying a ticket in advance for the Guggenheim (I did it just one or two days ahead).

In terms of crowding on the streets, it's really just a few areas where things are truly bad. There were lots of people in Piazza San Marco and in neighboring streets; it seemed worst to the east. The direct route from the train station to the Rialto Bridge on the east side of the Grand Canal has been a zoo for decades. Part of that route, the Strada Nova, is a major shopping street. Thinking back, I'm not sure I walked through the Rialto Market at all, so I'm not sure about that side of the canal.

I did a lot of walking around less touristy areas, including Canareggio and Dorsoduro, and the situation really wasn't bad. It's mainly the train station/Rialto/San Marco that are mobbed. Allow yourself plenty of time to wander freely of the well-trodden path and you can have a great time.

I was pleasantly surprised about the lack of crowding on Murano and Burano. Certainly there were other people around, but I expected much worse.

I think it helps a lot if you recognize that Venice is a highly popular city and are not expecting to get lost in a middle-age village. In addition, understand that all days are not the same. Special events or presence of multiple super-large cruise ships at the nearest ports could make a noticeable difference. We may have been lucky in our timing. However, the Art Biennale (a big deal) and Glass Week (a much smaller deal) were both occurring during our visit.