Fennec is likely the next best, although it lacks the Arkenfox hardening. Obtainium is a great app to get builds of Fennec directly.

If you're on GrapheneOS, there's Vanadium. Using a filtering VPN atop it can help reduce ads beyond what Vanadium can already block natively (the devs have integrated some lists that uBlock starts with, such as Easy List). This is the best option lieu of add-on like uBlock, which aren't supported.