Two external monitors from single Thunderbolt3 port (iMac 2017 21.5 inch non-Retina)?

Mirror only if I read correctly...

https://www.amazon.com/CableCreation-Compatible-Thunderbolt-Adapter-Chromebook/dp/B01M6C3B39/ref=asc_df_B01M6C3B39/?tag=hyprod-20&linkCode=df0&hvadid=309776868400&hvpos=&hvnetw=g&hvrand=4148727528688598510&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033327&hvtargid=pla-569549365633&psc=1

Or move the SSD to the xtra port on this...

https://www.apple.com/shop/product/HMX02ZM/A/caldigit-thunderbolt-3-mini-dock?afid=p238%7CstG6GNKNR-dc_mtid_1870765e38482_pcrid_407264219517_pgrid_85992530854_&cid=aos-us-kwgo-pla-btb-catchall--slid---product-HMX02ZM/A

https://eshop.macsales.com/item/OWC/TB3DK14PSG/?utm_source=google&utm_medium=shoppingengine&utm_campaign=googlebase&gclsrc=ds

If you can find real Thunderbolt displays with two Thunderbolt ports, like the LG UltraFine 4K Display

LG UltraFine 4K Display - Apple

you can daisy-chain two displays and other Thunderbolt devices using just one of the computer's Thunderbolt ports.

You may be an excellent candidate for a Dock. I would strongly recommend speaking to OWC (www.macsales.com) they have many solutions for Mac and specialize in them. Great company to deal with!