[Android Q&A, Help & Troubleshooting] tetratheta:
I have Teclast U10 Pro which is only available in South Korea.

This device is only available in South Korea. It is only listed in Teclast Korea homepage.

Teclast Korea don't provide download link of this device's firmware, and I don't think they will.

Last time I've contacted with them, which was 1.5 year ago, they said there are tecnical difficulties with providing firmware download because of Widevine L1 stuff.

I unlocked bootloader with this guide. Luckly, they didn't use different key for signing.

My goal are these:

Extract all firmware files as img files (for backup / failsafe)

Root my device via Magisk, which requires me to use boot.img or init_boot.img. (Ramdisk is Yes in Magisk)

But I don't get how and what to do for these.

Maybe using dd command to extract firmware would work. So I opened recovery log. Since I typed all of these by hand, there might be typo.

recovery filesystem table
=========================
0 /spl emmc /dev/block/mmcblk0boot0_a 0
1 /spl_bk emmc /dev/block/mmcblk0boot1 0
2 /uboot emmc /dev/block/by-name/uboot_a 0
3 /sml emmc /dev/block/by-name/sml_a 0
4 /tos emmc /dev/block/by-name/trustos_a 0
5 /teecfg emmc /dev/block/by-name/teecfg_a 0
6 /vbmeta emmc /dev/block/by-name/vbmeta_a 0
7 /vbmeta_system emmc /dev/block/by-name/vbmeta_system_a 0
8 /vbmeta_vendor emmc /dev/block/by-name/vbmeta_vendor_a 0
9 /vbmeta_product emmc /dev/block/by-name/vbmeta_product_a 0
10 /vbmeta_system_ext emmc /dev/block/by-name/vbmeta_system_ext_a 0
11 /dtbo emmc /dev/block/by-name/dtbo_a 0
12 /ltedsp emmc /dev/block/by-name/l_ldsp_a 0
13 /ltegdsp emmc /dev/block/by-name/l_gdsp_a 0
14 /lteagdsp emmc /dev/block/by-name/l_agdsp_a 0
15 /ltecdsp emmc /dev/block/by-name/l_cdsp_a 0
16 /ltemodem emmc /dev/block/by-name/l_modem_a 0
17 /ltefixnv1 emmc /dev/block/by-name/l_fixnv1 0
18 /ltefixnv2 emmc /dev/block/by-name/l_fixnv2 0
19 /ltedeltanv emmc /dev/block/by-name/l_deltanv 0
20 /lteruntimenv1 emmc /dev/block/by-name/l_runtimenv1 0
21 /lteruntimenv2 emmc /dev/block/by-name/l_runtimenv2 0
22 /wcnmodem emmc /dev/block/by-name/wcnmoden_a 0
23 /gnssmodem emmc /dev/block/by-name/gnssmodem_a 0
24 /pmsys emmc /dev/block/by-name/pm_sys_a 0
25 /misc emmc /dev/block/by-name/misc 0
26 /boot emmc /dev/block/by-name/boot_a 0
27 /persist emmc /dev/block/by-name/persist 0
28 /logo emmc /dev/block/by-name/logo 0
29 /fbootlogo emmc /dev/block/by-name/fbootlogo 0
30 /system ext4 system_a 0
31 /system_ext ext4 system_ext_a 0
32 /vendor ext4 vendor_a 0
33 /product ext4 product_a 0
34 /metadata ext4 /dev/block/by-name/metadata 0
35 /socko ext4 /dev/block/by-name/socko_a 0
36 /odmko ext4 /dev/block/by-name/odmko_a 0
37 /data f2fs /dev/block/by-name/userdata 0
38 /mnt/vendor ext4 /dev/block/by-name/prodnv 0
39 /storage/sdcard0 vfat /dev/block/mmcblk1p1 0
40 /tmp ramdisk ramdisk 0

So...

Is it possible to extract firmware from this information?

I've unlocked bootloader, but couldn't root my device because it requires me to use img from firmware.

Is it possible to create custom recovery from these?

I don't think stock recovery won't accept those extracted images unless I manually sign them. If I can create custom recovery like TWRP from those extracted firmware, I won't have to sign those firmwares.

PS. Yeah, I should've bought device from well-known manufacturer, but I didn't know that things whould be difficult at that time. I really regret my decision. But there is nothing I can do about it for now, right?