Although the model is no longer supported .... It is necessary to correct the source codes for this model, as the GPIO numbers do not match.
--- target/linux/ar71xx/files/arch/mips/ath79/mach-tl-wr841n-v9_old.c 2020-11-11 21:37:42.652784810 +0600
+++ target/linux/ar71xx/files/arch/mips/ath79mach-tl-wr841n-v9.c 2020-11-09 22:35:40.315725671 +0600
@@ -83,8 +83,8 @@
#define TL_WR740NV6_GPIO_LED_LAN4 11
#define TL_WR740NV6_GPIO_LED_WLAN 13
-#define TL_WR740NV6_GPIO_BTN_RESET 12
-#define TL_WR740NV6_GPIO_BTN_WIFI 17
+#define TL_WR740NV6_GPIO_BTN_RESET 0
+#define TL_WR740NV6_GPIO_BTN_WIFI 12
#define TL_WR841NV9_KEYS_POLL_INTERVAL 20 /* msecs */
#define TL_WR841NV9_KEYS_DEBOUNCE_INTERVAL (3 * TL_WR841NV9_KEYS_POLL_INTERVAL)