RE: Forwarded Emails From Dynamics 365 Marketing Missing Links
Hi,
No, not all links disappear when forwarding emails.
The link of SharePoint with permission settings may disappear due to security.
For example, here is a marketing email which contains a video, whose link is a fixed one and has no permission limit. When it is forwarded, it can also be shown in the receiver’s mail.

So, if you’d like to insert a link, for example, of a Teams Check-in, it is recommended to get the fixed link first and insert it directly instead of using the button or assist edit.
If this helped you, I'd appreciate it if you'd mark this as a Verified Answer, which may in turn help others as well.
Best Regards,
Nya