Is your Vegas Pro 19 under the subscription arrangement rather than having been purchased as a perpetual licence?
The reason being that Vegas Content is only available to Vegas 365 subscribers but not to those who purchased Vegas Pro as a perpetual licence. The following link is to the comparison webpage of Vegas Pro's different packages and purchase options With regard to Vegas Content, it was much the same with Vegas Pro 19.
The reason for this is that Vegas (MAGIX) has to pay the content providers for the content used by Vegas Pro users and onging subscription payments take into account the 3rd party content used. A perpetual licence can't take into account what content a user might access in years to come, content that Vegas (MAGIX) would have to continue to pay 3rd party content providers for - and that's not a good business proposition to say the least.