One of the devs replied to the discussion I started in the Mastodon repo:
https://github.com/mastodon/mastodon/discussions/36685#discussioncomment-14856034
One of the devs replied to the discussion I started in the Mastodon repo:
https://github.com/mastodon/mastodon/discussions/36685#discussioncomment-14856034
There are now two pull requests proposing changes to quote toots inside private mentions (DM).
[🟢 MERGED] When composing a DM, pasting a link will not create a quote: https://github.com/mastodon/mastodon/pull/36690
[🟢 MERGED] When composing a DM, it'll not be sent if it quotes a toot from someone not mentioned: https://github.com/mastodon/mastodon/pull/36689
The fixes are now merged into Mastodon's source code prior to v4.5 release 
If you have a fediverse account, you can quote this note from your own instance. Search https://bolha.one/users/cadusilva/statuses/115485894602339715 on your instance and quote it. (Note that quoting is not supported in Mastodon.)