Advise: Software to use for build a learning platform

Hello,
I try to find the right software to support a non-profit cross organizational learning platform. We need to manage multi-day workshops, split into intervals, where hosts, trainers & participants come from various independent organizations and assign themself via self service. Is there any open source LMS or CRM software, I can start with and extend? You find more details attached.
MS 365 and a WordPress Homepage (ucn-community.de) are available.
I’m thankful for any kind of advice.
Thanks and best regards, Matthias

do you know Moodle?

https://moodle.org/

I am not very sure though if that fits your necessity. But in my school, it’s being used to manage content for students.

Thanks a lot. I had a look at moodle and tried it out. Indeed, it offers a lot of the requirements.

Our core request is a list of all events, where hosts can assign themself to a three-day block, trainers to a certain day and parcitipants to all nine days. This kind of resource planning on different level seems not being supported.
How easy would it be to extend moodle (or a similar LMS) in this direction?

Thanks and best regards, Matthias