Advanced Features 

lib.contentElement.settings.media.popup {
    # Set custom CSS class for popup/lightbox links
    linkClass = lightbox
}

lib.contentElement.settings.media.popup {
    linkParams.ATagParams = class="fancybox gallery-item"
}

npm install photoswipe

page {
    includeJSFooterlibs {
        photoswipe = EXT:my_site/Resources/Public/JavaScript/photoswipe.min.js
        photoswipe_init = EXT:my_site/Resources/Public/JavaScript/lightbox-init.js
    }

    includeCSS {
        photoswipe = EXT:my_site/Resources/Public/Css/photoswipe.css
    }
}

lib.parseFunc_RTE {
    tags.img = TEXT
    tags.img {
        current = 1
        preUserFunc = MyVendor\MySite\UserFunc\LightboxImageRenderer->render
    }
}

namespace MyVendor\MySite\UserFunc;

use TYPO3\CMS\Core\Resource\FileRepository;
use TYPO3\CMS\Core\Utility\GeneralUtility;
use TYPO3\CMS\Frontend\ContentObject\ContentObjectRenderer;

class LightboxImageRenderer
{
    public function render(
        string $content,
        array $conf,
        ContentObjectRenderer $cObj
    ): string {
        // Check if zoom enabled
        if (strpos($content, 'data-htmlarea-zoom') === false) {
            return $content;
        }

        // Extract file UID
        if (!preg_match('/data-htmlarea-file-uid="(\d+)"/', $content, $match)) {
            return $content;
        }

        $fileUid = (int)$match[1];
        $fileRepository = GeneralUtility::makeInstance(FileRepository::class);

        try {
            $file = $fileRepository->findByUid($fileUid);
        } catch (\Exception $e) {
            return $content;
        }

        // Remove data attributes for frontend
        $content = preg_replace('/\s*data-htmlarea-[^=]+="[^"]*"/', '', $content);

        // Wrap in lightbox link
        $lightboxLink = sprintf(
            '<a href="%s" data-pswp-width="%d" data-pswp-height="%d" target="_blank">%s</a>',
            $file->getPublicUrl(),
            $file->getProperty('width'),
            $file->getProperty('height'),
            $content
        );

        return $lightboxLink;
    }
}

import PhotoSwipeLightbox from 'photoswipe/lightbox';
import 'photoswipe/style.css';

const lightbox = new PhotoSwipeLightbox({
    gallery: '.ce-bodytext',
    children: 'a[data-pswp-width]',
    pswpModule: () => import('photoswipe'),
});

lightbox.init();

lib.parseFunc_RTE {
    nonTypoTagStdWrap.HTMLparser.tags.img {
        fixAttrib {
            loading {
                set = lazy
            }
            # Remove internal attributes
            data-htmlarea-file-uid.unset = 1
            data-htmlarea-file-table.unset = 1
            # Keep zoom attributes for popup/lightbox rendering
            # data-htmlarea-zoom.unset = 1
        }
    }
}

<img src="..." loading="lazy" alt="..." />

page.includeJSFooterlibs.lazyload = EXT:my_site/Resources/Public/JavaScript/lazyload.js

lib.parseFunc_RTE {
    nonTypoTagStdWrap.HTMLparser.tags.img {
        fixAttrib {
            class {
                list = lazyload
            }
            data-src {
                # Copy src to data-src
                stdWrap.field = src
            }
            src {
                # Set placeholder
                set = data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 3 2'%3E%3C/svg%3E
            }
        }
    }
}

document.addEventListener('DOMContentLoaded', function() {
    const imageObserver = new IntersectionObserver((entries, observer) => {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                const img = entry.target;
                img.src = img.dataset.src;
                img.classList.remove('lazyload');
                imageObserver.unobserve(img);
            }
        });
    });

    document.querySelectorAll('img.lazyload').forEach(img => {
        imageObserver.observe(img);
    });
});