I've been using the official HORI lan adapter since I found it on clearance at a Walmart randomly. Currently they go for $30.
If you don't want to pay so much for first party, this one on amazon has a lot of positive reviews so I'd check it out https://www.amazon.com/UGREEN-Ethernet-Adapter-Nintendo-Chromebook/dp/B00MYT481C/ref=pd_lpo_23_t_2/139-4079997-8969305?_encoding=UTF8&pd_rd_i=B00MYT481C&pd_rd_r=c4795619-3a3e-4d46-989f-ec6d1f6e1404&pd_rd_w=Icl4L&pd_rd_wg=q4RUN&pf_rd_p=7b36d496-f366-4631-94d3-61b87b52511b&pf_rd_r=4Q2DMX00Y2AKVX902FGQ&refRID=4Q2DMX00Y2AKVX902FGQ&th=1