The current state of the device is shown bellow.
I prefer using heimdall to flash each partition directly from command line if possible. Unless it is mandatory to put all images inside a tar and flash them at the same time.
Top left corner of the Download mode screen:
More details of the previous (and solved) problem here: question
Flashing the correct img solved the problem:
heimdall flash --RECOVERY TWRP-3.3.1.0_A20_V1.2_by_Agrim720\[Black-themed\].img.img
File was found here: XDA-forum
Device: A205GUBU4ASK2
Previously rooted with boot.img patched by magisk and vbmeta flashed:
heimdall flash --BOOT magisk_patched.img
heimdall flash --VBMETA vbmeta.img
I highly recommend to avoid Samsung devices. Motorola ones, e.g. are better for custom ROMs.
If device complains about "official binaries", bypassing KG state is needed.
Q & A