I wanted to point out this thing because I'm in the middle of migrating my mail server and wanted to improve the whole setup by using chasquid and a set of dkim tools [1] that I've forked an improved to include ed25519-sha256. Unfortunately pretty much nobody has implemented RFC8463 yet, and my DNS provider doesn't allow me to use RSA 2048bit DKIM keys because they have a stupid limit on the TXT field value :(
You shouldn't rely on only ed25519 for DKIM, always double-sign your email with RSA as a fallback
The problem with email will forever be that there are so many badly configured email servers out there. Any new standard in email will always need a backwards compatibility ad infinitum.
In your case I'd recommend moving your DNS to another DNS provider. Just pick any and go with that.
[1]: https://github.com/denysvitali/dkim