If you take the route Google suggested at the moment (involving only funicular from Vallvidrera Inferior to Superior, then taking 111), you can use the Hola Barcelona Card.
The Hola Barcelona card includes public transport within Zone 1 (https://doc.atm.cat/ca/xarxa_ferrov_global.pdf), in which Tibidabo stop is situated.
Note though the Vallvidrera Funicular ...
From the U.S. Embassy in Spain (June 8, 2021):
At this time, we do not have additional details about which specific
vaccine certificates, such as those provided by the CDC, will be
accepted to allow entry for U.S. citizens into Spain. Please refer to
the Spain Travel Health portal (FAQs), and we will update our website
with this information as soon as it ...
For France, the way the rules have been phrased since last summer (so that's not changing as much as comments imply, even if some new development is always theoretically possible), the distinction has been based on where you are currently coming from / have been in the last 14 days. While non-essential travel is still not advised, there are currently no ...
It looks like this is allowable:
If the transit in Spain is carried out without leaving the international zone, you will not be required to present a AIDT. If the transit involves passing through border control centres and therefore entry into Spanish territory, they must present the boarding card or purchase ticket ...
you can pick up the card at the tourist information booth.
"You can also use your card to travel from Barcelona Airport. You can buy or pick up your card at the tourist information offices at the two terminals."
According to the purchasing site for Hola Barcelona, when you purchase the card online, you will be emailed a voucher code which you can use to retrieve the travel card itself at any metro station. They also offer a video about the process if that is interesting for you.
According to the same site, the card is valid for 72 hours (or your choice of other ...