Well, so far there are only people here saying how important this feature is to them and that they would donate X amount of money. However, no one has actually stepped up, neither to organize a way to collect donations nor to take on the actual work of developing this feature.
Therefore, the answers to those questions are simple: ‘Nowhere’ and ‘they cannot’. 
IIRC, this issue used to have a bounty on a bounty program website. But this issue has been open so long, that service closed doors since.
But, you are correct, there is currently nothing of the sort.
Part of the chicken and egg problem here is likely also that this is now a thread in a “Nextcloud freelancing” category on the official Nextcloud forum, so people may reasonably expect Nextcloud GmbH to manage the bounty part. Which seems not to be the case.
Hi all,
I was thinking on working on this but it seems that a Pull Request is up for review to add this functionality Support for recurring tasks by schulm · Pull Request #3021 · nextcloud/tasks · GitHub
Looks like schulm - Martin Schulze deserves a payout from the folks here. I’m testing after building the Git Clone, and works great so far in Nextcloud 33.0
In Pull request 3021, Martin provided a Paypal address. I’ve paid him my pledge. If you pledged money for this, please honor your pledges. It’s been 9 years since this was requested, in spite of allegedly being the single most requested item in the database. Martin came through for us, so let’s come through for him.
Hi guys, my paypal is:
Do you have an IBAN or Wise account or Venmo? PayPal is showing a $2.50 fee plus a crappy currency conversion rate. I can send euros directly but not via PayPal
I’ve allowed it in my Paypal settings, that venmo users can find me. Can you try it?
I don’t see anything different here. Perhaps you could post your venmo handle if you have one?
I’ve paid this now as well. Sorry that it took some time. Nearby, Paypal charged me 6,33 €. 