The best way to describe the Royal Blood sound is like a Siamese Dream-era Smashing Pimpkins meets Led Zeppelin or The White Stripes. The key is a single bass guitar split into two signals using a tuner or A/B into a higher octave or chord generator. We send the bass signal to a traditional rock bass setup, but the single-octave, double-octave, or octave-fifth chord are distorted and sent to an electric guitar amp. Without distortion, the setup approximates a 12-string bass.
Guitarists have used “octavers” for years. The pedal produces a lower octave note far simpler than a POG by halving the frequency, say from A440hz to A220hz, which is easily done. The POG artificially generates an octave higher using more complicated math, for example from A440hz to A880hz.
One key is to send the generator a smooth, round note, so there’s as little noise as possible in the octave generation process. Distortion and tubes are happy to restore some noise to the signal once the transition is complete. While killer bass tone is central to the formula, I’ll focus on the higher octave chain.
The Electro-Harmonix POG2 accomplishes this effortlessly. It tracks well, has a million options and tones, and costs nearly $400. A killer investment for Royal Blood, who tours with two on his board with different settings for the double-octave and the octave-fifth setting, which can also be accomplished with a Boss Octave OC-5 (with a new higher octave setting on the model #5) or Harmonist PS-6 ($135–155).
The ZOOM bass and guitar MultiStomp series contain pitch options that simulate these pedals as well as the tuner, splitter, EQ, distortion, and amp-simulation. BUT. These pedals have serious latency issues and do not track well. For around $99 they are indispensable for trying out sound concepts with dozens of stomp and amp simulators, but poor for tracking on account of a significant delay.
The best recommendations below have little or no latency or delay and track basically as well as their Electro-Harmonix and Boss counterparts.

VSN Guitar Octave Effect Pedal For Electric Guitar Precise Polyphonic Octave Effects Generator Octpus Guitar Pedals True Bypass Mini Size
Two higher octaves notes aka 1/2 octaves or 12/24 steps – Nails the classic Royal Blood tone.
VSN OCTPUS: https://amzn.to/3fAcc7h

Donner Digital Octave Guitar Effect Pedal Harmonic Square 7 modes
Single generated note alows the chord feature, ideally the 5th which works for most chords.
HARMONIC SQUARE: https://amzn.to/3oxyJ8Y

ammoon Precise Polyphonic Octave Generator Pedal
One higher octave, most expensive recommendation, but best looking and simple.
PRECISE POG: https://amzn.to/3fxOVmz

Zoom MS-60B MultiStomp Bass Guitar Effects Pedal, Single Stompbox Size, 58 Built-in effects, Tuner
ZOOM BASS: https://amzn.to/3bJ3baW

Zoom MS-50G MultiStomp Guitar Effects Pedal, Single Stompbox Size, 100 Built-in effects, Tuner