I would leave your Liquid Glass setting unchanged.
The almost-white vCard background with pale or nearly white lettering is consistent with a contrast or rendering problem in how the contact card is being displayed. The fact that it becomes somewhat easier to read against a darker background is also consistent with that observation, although it does not establish the cause.
First, quit Messages completely with Messages > Quit Messages (⌘Q), reopen it, and check the same contact again.
If it still looks the same, save the VCF and open it with Contacts.
Apple confirms that macOS can import .vcf files into Contacts: Apple — Import contacts into Contacts on Mac.
If it is readable there, that would indicate that the VCF itself can be displayed normally in Contacts and that the problem may be associated with how Messages is displaying the contact card.
The next useful test is to receive or open another contact shared as a VCF.
If another VCF displays normally in Messages, the problem may be specific to the original contact file.
If multiple VCF contact cards have the same pale-text-on-light-background appearance, that would provide more evidence of a Messages rendering issue.
I would not change Liquid Glass, transparency, contrast, or other system-level settings at this point.
One other thing that may be relevant, although I would not assume that it is related to this particular problem, is that macOS Tahoe 26.7 was released on September 14, 2026. Apple lists numerous security fixes in that update.
If you are currently running 26.6, it would therefore be reasonable to install 26.7 before doing more extensive troubleshooting.
However, Apple’s published information does not establish that 26.7 specifically addresses the pale-text-on-light-background appearance of VCF contact cards in Messages.
Apple — About the security content of macOS Tahoe 26.7
