const spawn = () => {
    const dinoRight = document.getElementById('dino').getBoundingClientRect().left + document.getElementById('dino').getBoundingClientRect().width;
    const dinoLeft = document.getElementById('dino').getBoundingClientRect().left; 
    const dinoHeight = document.getElementById('dino').getBoundingClientRect().height;
    const cactusTop = document.getElementById('cactus').getBoundingClientRect().top;
    const cactusWidth = document.getElementById('cactus').getBoundingClientRect().width;
    const containerLeft = document.getElementById('Container').getBoundingClientRect().left;
    cactus1move(dinoRight, dinoLeft);
}


//not sure if you can pass it directly to the interval
    const cactus1move = setInterval((dino_right, dino_left)=>{
        if (cactusTop<=dinoBottom&&dinoRight>=cactusLeft&&cactusRight>=dinoLeft) {
            ...
        } else if (cactusLeft<=containerLeft+10&&cactusLeft>=containerLeft){
            ...
        } else {
            ...
        }
    },20)


//if it does not work you can pass the parameters to a function and then down to the interval
    const cactus2move = (dino_right, dino_left)=> {
        setInterval((dino_right, dino_left)=>{
        if (cactusTop<=dinoBottom&&dinoRight>=cactusLeft&&cactusRight>=dinoLeft) {
            ...
        } else if (cactusLeft<=containerLeft+10&&cactusLeft>=containerLeft){
            ...
        } else {
            ...
        }
    },20)}

In your code, variables are declared inside the functions (i.e the scope of these variables is restricted to function). You can declare these variables outside the functions so that both the functions will have access to it. Your code will go something like:

    let dinoRight, dinoLeft, dinoHeight, cactusTop, cactusWidth, containerLeft;
const spawn = () => {
        dinoRight = document.getElementById('dino').getBoundingClientRect().left + document.getElementById('dino').getBoundingClientRect().width;
        dinoLeft = document.getElementById('dino').getBoundingClientRect().left; 
        dinoHeight = document.getElementById('dino').getBoundingClientRect().height;
        cactusTop = document.getElementById('cactus').getBoundingClientRect().top;
        cactusWidth = document.getElementById('cactus').getBoundingClientRect().width;
        containerLeft = document.getElementById('Container').getBoundingClientRect().left;
        cactus1move();
    }
    const cactus1move = setInterval(()=>{
        if (cactusTop<=dinoBottom&&dinoRight>=cactusLeft&&cactusRight>=dinoLeft) {
            ...
        } else if (cactusLeft<=containerLeft+10&&cactusLeft>=containerLeft){
            ...
        } else {
            ...
        }
    },20)

You can pass parameters when calling the method, so that it can be used inside the method. If it is not necessary, I recommend not to use global variables to get the value.

In the following code, I call cactus1move passing the value and wrap the value into an object. When implemented inside cactus1move, I use destructuring assignment to get the value out of the object, and then you can use these values to do something.

const spawn = () => {
  const dinoRight = document.getElementById('dino').getBoundingClientRect().left + document.getElementById('dino').getBoundingClientRect().width;
  const dinoLeft = document.getElementById('dino').getBoundingClientRect().left;
  const dinoHeight = document.getElementById('dino').getBoundingClientRect().height;
  const cactusTop = document.getElementById('cactus').getBoundingClientRect().top;
  const cactusWidth = document.getElementById('cactus').getBoundingClientRect().width;
  const containerLeft = document.getElementById('Container').getBoundingClientRect().left;
  cactus1move({
    dinoRight,
    dinoLeft,
    dinoHeight,
    cactusTop,
    cactusWidth,
    containerLeft
  });
}

const cactus1move = (data) => {
  return setInterval(() => {
    const {
      dinoRight,
      dinoLeft,
      dinoHeight,
      cactusTop,
      cactusWidth,
      containerLeft
    } = data;
    console.log('dinoRight', dinoRight);
    console.log('dinoLeft', dinoLeft);
    console.log('dinoHeight', dinoHeight);
    console.log('cactusTop', cactusTop);
    console.log('cactusWidth', cactusWidth);
    console.log('containerLeft', containerLeft);
  }, 2000);
}

#dino {
  width: 80px;
  height: 80px;
  background-color: #FFBB73;
  float: left;
}

#cactus {
  width: 90px;
  height: 90px;
  background-color: #FFBB33;
  float: left;
}

#Container {
  width: 100px;
  height: 100px;
  background-color: #FFBB13;
  float: left;
}

<div id='dino'></div>
<div id='cactus'></div>
<div id='Container'></div>
<button onclick="spawn()">spawn</button>