This site lists the communities on -shall not be named- that have either migrated or are also located on different sites. It also lists whether it is the official community or a spin off. A very helpful tool for those who have rid of -shall not be named- and have forgotten communities they once followed.
"A causa della protesta in corso contro i nuovi termini API di Reddit, molti subreddit sono privati o limitati. sub.rehab elenca le istanze delle comunità Reddit su piattaforme alternative"
When Sync for Reddit show a popup promoting Sync for Lemmy, it should also point to this kind of service, to ease the migration.
It would also be nice, if sync for Lemmy also had a shortcut.
Besides that a link to a more general community directory like https://lemmyverse.net/ would be nice to have.
There are lists that provide the equivalent communities to Reddit subs. It should aid discovery and help provide a more seamless user experience for those who have yet to make the jump, so consider adding any communities that you start: