Sell your old 16GB RAM.

Sell it. Even old DDR3 or DDR4 sticks have a good secondhand market. Somebody building a budget rig or upgrading an old office PC will happily pay $30–50 for a single 16GB stick.

eBay and Facebook Marketplace are fine. Just check your RAM generation (DDR3 vs DDR4) and speed before listing — or include a photo of the label.

Don’t overthink this. It’s not obsolete. It’s just not right for your machine anymore. Someone else’s machine needs it.