i wanted to ask if sh404sef would be compatible with Joomla 4 or if it will become?
It isn't and won't be made compatible, that would required a full rewrite which did not make any sense. Instead, we have created 4SEO which is focused on SEO-only and as such is much more advanced than sh404SEF in that field: it's all the SEO of sh404SEF plus structured data, sitemaps generation, broken links detection, full content replacer and many more smaller things.
As you read, the SEF URLs features of sh404SEF will be made into 4SEF. 4SEF will only do SEF URLs, ie creating them automatically and allow customization. It will be a replacement for sh404SEF both on Joomla 3 and 4, but without any other type of SEO features such as canonical or redirects (which are in 4SEO).
Moving from sh404SEF to 4SEF will be transparent: install 4SEF and disable sh404SEF, that's all. This should be done in Joomla 3, before you upgrade to Joomla 4 but can also be done directly in Joomla 4, provided that the database tables and configuration files are left in place after the migration to Joomla 4.
Note that any redirection or custom meta data can only be transferred to 4SEO as 4SEF will only take care of SEF URLs. This also will be transparent (ie, 4SEO will detect and use sh404SEF custom data found, if any).
As for a deadline, development of 4SEF is just starting and I plan on releasing it as stable during the last quarter of 2021, with beta testing during a month or 6 weeks before stable release, as we did for 4SEO (although 4SEo was larger and more complex).
Hope this covers it all, thanks for your continued use of sh404SEF!
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