The ROAS in the ad set is decreasing. Should we just shut it down or try to make new content and try again

From your metrics seems your CPC link is 1 euro+ and your CTR link is 1.8%. Which tells me your creative/ ads isn’t strong enough to be competitive.

With that being said you are getting sales, so I would just duplicate this adset and add new creative to it to test and get it to benchmarks we have established as a standard – Facebook Ads KPIs Cheatsheet