Only 1x DDR4 module
Did I make a mistake of only buying 1x DDR4 module?

My LGA2066 MOBO keeps mentioning 44 lanes, 28 lanes or 16 lanes...

I hope you will learn to understand that you are asking the "wrong questions" . You can't really ask if something is enough without giving the whole specs of your system. What should we answer if you didn't provide the details of the rest of your system ?

So the only correct answer would probably just be: "it depends".

also what does "1x DDR4 module" even mean ? Are you talking about some specific memory amount in GB ?
Of course there exists also 64 GB modules for instance (in general), but it all depends what your CPU and GPU specs are.

Which GPUs ? How many of them ? How much VRAM (video RAM, device RAM) do they have .

In general, you would need at least this:
total RAM on host is more than the sum of all devices VRAM (GPU)

This is needed because the drivers/runtimes are mapping VRAM to RAM an therefore having too little RAM is very bad for performance (swapping to disk) and often does not even work (memory problem when starting OpenCL kernels and hashcat) because the RAM/mapping can't be allocated.
My specs are:

1x Kaby Lake X 7640x cpu
1x DDR4 2133 mhz ram
2x RTX2080 TI
1x 5200 RPM SATA HDD
1x 1000 watt PSU
1x Gigabyte X299 UD4 MOBO
what type/model of RAM and how many gigabytes (GB) of RAM ?
G.SKILL Aegis 16GB 288-Pin DDR4 SDRAM DDR4 2133 (PC4 17000) Desktop Memory Model F4-2133C15S-16GIS