You can enable shares with a USB 3.0 drive using Ksmbd, or if you want more advanced features Samba, they perform similar: https://openwrt.org/docs/guide-user/services/nas/ksmbd
Performance is great, most targets from the past half decade can read/write at 100MB/s (nearly saturating gigabit lan) including R4S (e.g. I'm getting >100MB/s with GL-MT6000 and my old WRT32X did 110MB/s).