Most of them will work out of the box. I have use the following:

https://www.amazon.com/gp/product/B09WJ12T78/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B087QZVQJX/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I did not test multi monitor support, but recall that Chromeunbox reported that each chromebook can support up to 3 monitors.

On the kids Acer Spin 513, only one of the USB C outputed video. If you don't get video out of one, try a different port.