您的解决方案几乎是正确的。您只是不了解<link>id的用法，但没有问题，让我快速为您总结一下：

1.）需要一个新的引用元素到主题css文件。

第二部分是使theme.css可通过链接元素访问...

<!-- Add default theme url to href | now default is light -->
<link id="id-to-link" rel="stylesheet" href="/themes/lara-light-purple/theme.css">

2.）在函数中使用your-id作为第三个参数。

...这样链接的id就可以作为第三个参数提供给changeTheme函数。

// if current theme is dark
const selectLightTheme = () => {
    // 1. Current theme name
    // 2. Next theme name
    // 3. id of <link>, what reference to where set theme css file
    PrimeVue.changeTheme('lara-dark-purple', 'lara-light-purple', 'id-to-link', () => {});    
}

// if current theme is light
const selectDarkTheme = () => {
    // 1. Current theme name
    // 2. Next theme name
    // 3. id of <link>, what reference to where set theme css file
    PrimeVue.changeTheme('lara-light-purple', 'lara-dark-purple', 'id-to-link', () => {});
}

来源于文档：https://primevue.org/theming/

如何动态制作？

<!-- Add default theme url to href | now default is light -->
<link id="id-to-link" rel="stylesheet" href="/themes/lara-light-purple/theme.css">

import { ref } from 'vue';
import { usePrimeVue } from 'primevue/config';

// set default theme folder-name to currentTheme
const currentTheme = ref('lara-light-purple'); // lara-light-purple or lara-dark-purple (1st parameter)

const PrimeVue = usePrimeVue();

// change current theme to next
const toggleTheme = () => {
    // What is next theme? (2nd parameter)
    let nextTheme = 'lara-light-purple';
    if (currentTheme.value === 'lara-light-purple') nextTheme = 'lara-dark-purple';
    else if (currentTheme.value === 'lara-dark-purple') nextTheme = 'lara-light-purple';

    // 1. Current theme name
    // 2. Next theme name
    // 3. id of <link>, what reference to where set theme css file --> fix, single id to <link>
    PrimeVue.changeTheme(currentTheme.value, nextTheme, 'id-to-link', () => {});    

    // So current theme now:
    currentTheme.value = nextTheme;
}