[Question] Best architecture to support multisite

[whuu]

What is the suggested/best strategy for the front-end head project to work with headless CMS backend hosting multiple sites?
Assumption:

• all sites will share most of the blocks.
• all sites will share the most of the business logic.
• each site will have different content and assets (but some may be shared).
• each site will have a different theme (most of the CSS will be totally different).

Which approach is possible and recommended?

1. Bundle everything into one Next application and choose different CSS theme on runtime based on domain/site setting. This might lead to unused CSS, but on the other hand there is only one front-end app deployed to hosting provider (like DXP) so the setup is simple.
2. Customize bundling of Next application, so during build time only selected CSS theme will be bundled into build package. This would be more optimal from lighthouse score perspective, but it would require multiple front-end apps built and deployed to hosting provider. Would DXP support it? (assuming some adjustments to headless proxy).
3. Have different front-end code for each site (I guess this would be overkill if the only difference between sites is CSS theme, in terms of the deployment and hosting it will similar in the end to point no.2).
4. Other approach?