How to use async/await in the best way Protractor

I was trying to use .then() with my test cases but without success because of strage comportament. I'm trying make tests with google chrome to.

i have the "SELENIUM_PROMISE_MANAGER: false," in my conf.js file.

Now the problem:

When i trying to find some elements in the DOM i has problems...the actual error is:

Failed: Index out of bound. Trying to access element at index: 2, but there are only 0 elements that match locator By(css selector, .mat-option-text)

The CODE (With comments)

    console.log('Testing Pesquisa Assunto ...');
    beforeAll(function () {
        var teste = browser.get(browser.params.URL_PROCESSO).then(function () {
        })
    });
    it('Deve escolher um ASSUNTO PRINCIPAL e verificar os resultados', async function () {
        try {
            if (browser.findElements(by.id('filtro_assuntos')).toEqual(""));
        } catch{
            await element(by.id('maisFiltros')).click()
            await element(by.className('[placeholder = "main"]')).isPresent()

            try {
                //THE TEST DON'T DO ANYTHING OF THAT 
                await element(by.css('[placeholder = "Assunto"]')).isDisplayed()
                await element(by.css('[placeholder = "Assunto"]')).click()
                await element(by.className('cdk-overlay-pane')).isDisplayed();
            }
            catch{
                //THE TEST IS ENTERING HERE
                console.log('Cannot find a list ') 
            }

            var clicaAssunto = await element.all(by.className('mat-option-text')).get(2).click(); //AND HAS PROBLEMS TO FIND THIS LIST OF OPTIONS
            await element(by.className('mat-slide-toggle-bar')).click()
            await element(by.className("aplicar")).click()
            await element(by.className('processo')).isPresent()
            await element(by.className('identificacao')).isPresent()
            await expect(element(by.className('identificacao')).getText()).toContain('Abandono');
        }
    })
});```