from what I tested every link in supported site in danbooru instances fallback to generic downloader and only download the first page of the link also with danbooru that show 403 forbidden not entirely sure but could be duplicate of #6594. Also does regression mean use the older version?
log:
[gallery-dl][debug] Version 1.28.0-dev
[gallery-dl][debug] Python 3.12.4 - macOS-15.0.1-arm64-arm-64bit
[gallery-dl][debug] requests 2.32.3 - urllib3 2.2.3
[gallery-dl][debug] Configuration Files ['${HOME}/.config/gallery-dl/config.json']
[gallery-dl][debug] Starting DownloadJob for 'https://aibooru.online/'
[generic][info] Falling back on generic information extractor.
[generic][debug] Using GenericExtractor for 'https://aibooru.online/'
[urllib3.connectionpool][debug] Starting new HTTPS connection (1): aibooru.online:443
[urllib3.connectionpool][debug] https://aibooru.online:443 "GET / HTTP/11" 200 None

Another one with danbooru:
[gallery-dl][debug] Version 1.28.0-dev
[gallery-dl][debug] Python 3.12.4 - macOS-15.0.1-arm64-arm-64bit
[gallery-dl][debug] requests 2.32.3 - urllib3 2.2.3
[gallery-dl][debug] Configuration Files ['${HOME}/.config/gallery-dl/config.json']
[gallery-dl][debug] Starting DownloadJob for 'https://danbooru.donmai.us/'
[generic][info] Falling back on generic information extractor.
[generic][debug] Using GenericExtractor for 'https://danbooru.donmai.us/'
[urllib3.connectionpool][debug] Starting new HTTPS connection (1): danbooru.donmai.us:443
[urllib3.connectionpool][debug] https://danbooru.donmai.us:443 "GET / HTTP/11" 403 None
[generic][warning] Cloudflare challenge
[generic][error] HttpError: '403 Forbidden' for 'https://danbooru.donmai.us/'
[generic][debug]
Traceback (most recent call last):
File "/miniconda3/lib/python3.12/site-packages/gallery_dl/job.py", line 151, in run
for msg in extractor:
File "/miniconda3/lib/python3.12/site-packages/gallery_dl/extractor/generic.py", line 69, in items
page = self.request(self.url).text
^^^^^^^^^^^^^^^^^^^^^^
File "/miniconda3/lib/python3.12/site-packages/gallery_dl/extractor/common.py", line 242, in request
raise exception.HttpError(msg, response)
gallery_dl.exception.HttpError: '403 Forbidden' for 'https://danbooru.donmai.us/'