Is the Barcelona city pass worth it?

Is it the Barcelona Card you're considering? I took a look at its features back in March and posted some comments in this thread: https://community.ricksteves.com/travel-forum/spain/barcelona-card-530da346-926a-459f-8269-0df7eff7194e

In summary, it didn't look like a good deal to me.

Barcelona sightseeing is expensive. A lot of the most popular sights seem to be privately operated rather than government run, so there's not much focus on keeping them accessible for those who are not so affluent.

The top sights tend to get overrun, so a crowded viewing experience may be a given. What you don't have to do is waste hours in each ticket line. Buy tickets ahead of time for any of these places you decide you want to see:

La Sagrada Familia
Casa Mila/La Pedrera
Casa Batllo
Parc Guell
Picasso Museum
Palau de la Musica Catalana (English tours can sell out)

I haven't read anything on this forum that makes me think tickets need to be purchased way ahead of time; I don't think those places have been totally selling out far ahead of time. (You can and should check the ticket situation for each sight. Are any time slots selling out early? My visits to the listed sights were back in 2015.) It's more that if you show up without a ticket, you will probably be in a very long line and the first ticket available may be for several hours later--or the next day if you show up late in the afternoon. That makes for very inefficient and frustrating sightseeing.

Tickets are available online for all of the above places. I haven't checked recently, but there might be a slight discount for buying an online ticket. It is annoying to have to pin down entry times for multiple sights on the same day. How much time do you need to leave between them so you have all the time you want at Sight #1 but won't waste a lot of time by allowing an excessive gap? That's basically an unanswerable question. Therefore, I highly recommend taking advantage of every day you wake up in Barcelona by purchasing a first-time-slot ticket for one of your top-priority sights. That way, at least for those sights, you won't have to worry about rushing away from something else you're enjoying in order to be on time. A side benefit is that when you walk in, there will not already be hundreds of other visitors (who had earlier entry times) clogging the space. I found this made a really big difference at La Sagrada Familia.

There are lots of worthwhile sights in Barcelona that are less busy and haven't required pre-purchase of tickets in the past. (This situation could change.) Just a few of those are the Sant Pau Modernista Site, the Miro Museum and the MNAC art museum.

Walking around, playing "spot the wacky modernista architecture", is free. That game is best played in the Eixample. Walking around the Barri Gotic is free. The Magic Fountain on Montjuic (near the MNAC and Miro Museums) is free.

I thought the tourist office's walking tour of (part of) the Barri Gotic was excellent. It's not free, but it's low-cost. The tour group was considerably smaller than those on the so-called "free" tours.

Barcelona has an excellent subway system if you get tired of hoofing it. On the day I arrived in the city, I saw a line of people at the Placa de Catalunya hop-on/hop-off bus stop that was so long it clearly was going to take two buses to accommodate all of them; there was no bus visible, so the HO/HOs didn't seem like a great idea to me.

One other comment about the financial side of visiting Barcelona: Many restaurants (I suspect most) have special deals at lunchtime, making that a less expensive time of day to have your main meal. Look for sandwich boards or chalkboards outside the restaurants. As always, avoiding restaurants right near major tourist sights is likely to save money.

My two cents...

City Pass: I agree with Anne, it's hardly ever worth it as you're unlikely to save much, if anything, in the major sites and to save in the less touristy sites you'd need to visit a bunch of them... which you won't have time anyway (most likely!).

Transportation: If you want to save yourself some money, these days I'd go for the T-FAMILY card. Google for it and notice its restrictions. There are several transportation cards, not getting now into the ins and outs, I personally believe the T-FAMILY is the most convenient for the casual group of visitors to the city. Hohos are not included with any transportation card, they require a separate ticket, and it's expensive. Unless you're in for a "bus tour", I wouldn't use it as means of transportation to get from A to B.

Food: as pointed, "menu del dia". Most restaurants offer it Mon-Fri and it consists of a three-meal course for under 15€ (in most places anyway). Forget sandwiches, burgers and other trash food and eat properly by having a menu-del-dia... as grandma would say!

Crowds: that's what it is, darling. Being one of the most popular destinations in Europe for decades has its tolls... and crowds are one of them. We residents know (and suffer them too!).

Skip-the-line promises: there's no such thing if anyone tries to sell you that you're being taken for a ride with a marketing gimmick. I've seen this, especially in foreign sites selling "Barcelona passes", while the passes might be legit (they are resellers after all), the claims are not, or they're rather malicious. Let me explain: in many attractions there tend to be two lines, one for purchasing the ticket and another one to get in. Regardless of whether the site is first-arrived first-served or whether it requires to pre-book a time slot, there's going to be always a line to get in, either from someone who arrived before you or from other people that pre-booked the same time slot. BUT if you bought the tickets online, you won't have to line up on the first line (the one for the ticket booth) and can go straight to the second line, the one to get into the attraction. Thus, this is not really "skipping-the-line" as in whisking in front of everybody into the attraction but saving yourself having to do the first line -the one to buy the ticket. But you'll still have to line in the second one!.

Heat: if you're visiting in summer and if you come from moderate mild latitudes don't forget to hydrate yourself often by drinking lots of water, Barcelona is hot (32-36C) and can be very humid (+80%). You don't want to faint and spoil the day, right? :))