This YouTube video explains that to add a library's functionality to Tinkercad you actually have to copy/paste the contents of the library's .h and .cpp files into the sketch.
Is that the only way to do it? Big pita to do that for all my sketches which for example use the hd44780 I2C LCD library.... is there no way to actually add a library to Tinkercad?
Probably a question for Tinkercad's forum/customer support.
That is the only way 
Wokwi 
on the other hand, can select a library from the list which is used in the Arduino IDE Library Manager. If that is not enough, then multiple files can uploaded at once. If that is not enough, additional files (in their own tab) can be created and code can be copy-pasted into it. If that is not enough, you can ask the maker to add things, and maybe put money on it (see the Wokwi roadmap)
Wokwi can not simulate a analog circuit and there can be only one Arduino board. But it can connect to a serial port on your computer (Using the Chrome Serial API) and there is a Logic Analyzer which can capture digital signals to be analyzed on your computer.
Obviously, and a typically useless snotty Arduino forum answer. Even if one asks in the Tinkercad forum, there's no harm asking here, where there are many Tincercad users some of whom might actually have an answer. (Like Koepel, for example.)
I feared as much thanks- I was also going to look at Wokwi, which seems a better bet.
But any sim is better than the way I have to hunt around for components in my real life storage (not-a-)system.
Eh? What makes you think that my response was 'useless snotty Arduino forum answer'?
A number of users will ask this type of question, without going to the publishers website for a specific piece of software or core. The best place to ask specific questions is on their website/forum as even experienced Arduino users who use these packages may not know the software well enough to give a response.
Also, the BEST place to ask support questions is on the publishers site, as the answer would be available to other users of that software, should they have a simmilar issue.
I'm sorry if you felt my response was useless & snotty but it was offered with a genuine intent to help.