I am not sure about availability of such platforms, but if you wish to freelance, you can contact to companies which provide such services and give them a proposal, they will definitely consider for taking your services if they had work loads.
Contacting to companies means, you need to express your services in better way so that they could get confidence to offload you.
If they get a feeling of when work is given to you, instead of getting that completed they need to train you and by providing work to you actually they are running more short on time for providing training and correcting in works done by you, they most probably not going to respond.
So presentation and delivery of the services is also important parameter.
whatever work you are asking is directly related to finance / budget of that company, any mistake in calculation might be mistake for you but it will be a big mess for the owner.
An architect can remove wall, building or any part of structure just by erasing line what he drawn. further to this, no mistake can be tolerated as mistake. because doing that after execution increases very high cost.
So if you are targeting for getting freelance work, you need to express what benefits they will get by offloading their works to you.
Hope this will help you in getting some freelance work.
Such platform is available for Structural design, WTP and STP design etc only. One can avail/conduct online paid lectures on different subject, but certainly its doubted that during this bad period one could attain paid lectures.