La meditacion no es algo que puedas hacer;
Why is puedas used here instead of puedes? And why?
The short answer is that the word "no" in the primary clause
La meditacion NO es algo
negates what comes in the subordinate clause
que puedas hacer
thus requiring the subjunctive.
But why? What does this mean? The best answer in my opinion (there is more than one theory) is to be found in the explanation given by Ruiz Campillo. He states that the subjunctive is used when one does not wish to "declare" anything in the subordinate clause.
What does "declare" mean in this context? Well, when you "declare" something in the subordinate clause, basically you're saying "this thing is true". In Spanish, according to Campillo, this is a bit of a contradiction:
?? No creo que vas a la fiesta
doesn't make sense then, because at the same time you're saying to someone that you don't believe they're going to go to the party, by using the indicative "vas", you're also DECLARING that they ARE going to the party. Here is, according to Campillo, where the subjunctive comes in.
No creo que VAYAS a la fiesta
Now you're NOT DECLARING anything about them going to the party, you're simply saying that you don't believe that they're going. VAYAS, here, isn't expressing an opinion on the matter in the same way that VAS does -- think of the subjunctive, in this context, like "hedging your bets", not "declaring" anything.
So in your phrase, you wouldn't want to say
?? La meditacion no es algo que puedes hacer
because in that phrase you're both saying that you don't think meditation is something that the person can do, but also, by using the indicative 'puedes', DECLARING that the person can do it. You don't want to say that they are able to meditate. You don't want to DECLARE that. So you use the subjunctive, so as not to declare that they can do it.
(Of course in English, and in German, we have no problem with this, but then we don't really have the subjunctive: to us saying "I don't believe you are going to the party" seems perfectly normal, it's just that Spanish allows a greater deal of expression using the subjunctive).
I highly recommend you check out Campillo's work -- once you understand it you will (largely) understand the subjunctive. His 'declaration' theory works for most of the cases where you'd use the subjunctive.
For an animated intro to his theory on the subjunctive, check out https://marcoele.com/el-subjuntivo-es-logico/ (you need to click on the purple images).
For a more in-depth discussion, see this page on his website (you'll need to be able to read Spanish -- I haven't found his work in English, but since he teaches at Columbia Univ, I suspect it's out there somewhere).
Finally, if you want to read the original academic paper in which he outlines his theory, you can find it here.