Look into invoice factoring services. You sell your invoices to them and get paid upfront. They get a % of your invoice and/or a small processing fee.

Ideally you want a non-recourse factoring agreement (the one where the factoring company takes most of the risk of non-payment), but it might be difficult to get. It helps if you can show that your previous clients paid on time. But then again the freelancing platforms handled that for you.

In any case, it's worth asking around. Have your lawyer review the factoring terms before you agree to anything.