Ignat Korchagin from Cloudflare has created a patch to improve the performance of dm-crypt considerably, see
https://github.com/cloudflare/linux It seems they run this patch themself in over 200 datacenters.
Perhaps the Debian-kernel maintainers would consider creating a 5.4 amd64 kernel-package with this patch implemented. Just as linux-image-5.4.0-0.bpo.4-amd64 package in buster-backports repository.
In the light of SEDs (self-encrypting drives) the latest years have turned out to be less secure than expected, dm-crypt is more relevant than ever ;-)
Best regards
Brian Wengel, Denmark