Finally I identified serial myself as on the picture below. Board has three TTL serials: J3 (UART0), J47 (guess) and J60 (guess) with voltage level 3.4V which is fine for my USB CP210X dongle. Kernel console is available on UART0 (115200 8N1, no flow control) and provides standard HiLinux syslog and ...

Fennec62, i have this doorbell https://fr.aliexpress.com/item/Smart-720P-Home-WiFi-Video-Door-phone-intercom-Doorbell-Wireless-Unlock-Peephole-Camera-Doorbell-Viewer-220v/32762916125.html?spm=a2g0s.9042311.0.0.2d2a6c37UmFt4B i find RX and TX on motherboard so i active telnet Me probably too ...