https://www.amazon.com/NETGEAR-AC1200-Wi-Fi-Adapter-A6210-100PAS/dp/B00MRVJY1G/ref=sr_1_2?dchild=1&keywords=netgear+wifi+A6210&qid=1630361261&sr=8-2 Has worked really well for me be it on 20 or 21.
I'd recommend this Netgear USB 3.0 / AC1200 for $26
Since it's 2017, it's a good idea to get something dual-band, 802.11ac-capable, capable of at least 2 spatial streams, and that uses USB 3.0 or better (USB 2.0 is too slow to keep up with 802.11ac dongles). Netgear is a long-established brand name in home networking, and hopefully that $26 price doesn't break the bank.