The platform that works closest to this is https://www.liberapay.com/
It used to allow making 1 monthly payment and spreading it between projects. But they had to change to comply with banking/payment platform rules so each money transfer is directed to one beneficiary from the get go. Meaning you setup a recurring payment per project.
There's also the nlnet foundation https://nlnet.nl/
It's possible to give them 1 recurring payment to support OSS projects. But they manage how the money is split between projects and their own overhead. You don't pick the projects.