This forum post will help. You can buy Crucial RAM and it is compatible with Dell systems. However and this is an important point, only Dell supplied RAM will run as XMP, 3rd party RAM is not supported. 3rd party RAM will run at 2666. The above mentioned post has more information. It may work but Dell will not support the RAM if you have a problem.

Hi @INXSEX  the RAM speed is limited by what the CPU will support. Dell Support for Area-51m R2 says the two Memory slots will support 64GB (2x 32GB), SoDIMM DDR4, 2933MHz, dual-channel. 

Goat From CT called Dell Tech Support to ask about RAM upgrade to Corsair Vengeance Performance, 64GB (2x 32GB), 3200MHz. Dell said BIOS is not locked, user can turn on XMP in the BIOS and run these at 3200MHz. Dell just won't support it (won't help troubleshoot it) until user takes out RAM upgrade and revert back to the original as supplied by Dell configuration. Only then will Dell support this system again. 

There is limited room inside the laptop, be careful to get thermal shield whose height will fit. 

Hello i finally found compatible Dell memory:

https://www.amazon.com/dp/B08SBSDNJN/ref=cm_sw_r_cp_awdb_imm_2EG8ZPBM75NHCWKAV18R

Is 32gb RAM compatible for Área 51m R2, is a copy of the actual Dell RAM.

It will take a little bit of time before they arrive, but its half the price of Dell RAM, let you know how they perform when they arrive.

How did this ram upgrade work out?

Hi @INXSEX & @Bifocal Bensch the Crucial System Advisor database is a good source of information Alienware Area-51m R2 | Memory RAM & SSD Upgrades | Crucial.com.