Does the Electro-Voice RE20 need a Cloudlifter?
Yes. With the Cloudlifter CL-1 already in line, the Scarlett Solo (Gen 3) only has to supply about 32 dB of the 56 it publishes. Published numbers only.
The hard gain is already done. The Cloud Microphones Cloudlifter CL-1 sits in front of the Focusrite Scarlett Solo (Gen 3), so the interface preamp is no longer the thing that has to rescue a quiet microphone.
Electro-Voice rates the RE20 at -56.5 dBV/Pa, the voltage from a loud 94 dB tone at the grille. A speaking voice is closer to 85 dB, so the preamp still has to find about 32 dB to land near −9 dBV. That −9 dBV figure is just a tracking level: high enough to use, with space before the converter clips.
Feed the interface from the booster's output and do not stack a second microphone preamp on top. Most inline boosters spend the 48 V themselves. That is fine for a dynamic. If this microphone is a condenser, read the booster's manual before you leave it in the chain: if it does not pass phantom, the capsule goes silent.