The fitness fashion of the 90's was reasonably pro cardio, while the 2010's went the opposite direction. As I hit middle age, I am starting to notice the consequences and think it is time to hit something as simple as a bike / cross trainer to get some high heart rate work in regularly.

Cardio will impact your gains but that shouldn't matter to you unless you're trying to maximize muscle growth.

Exactly my point, yeah. The significance of the impact is also debatable and not nearly as much as one might think, especially if you do proper programming.

I don't lift weights to compete, I lift to be healthy, strong and generally fit. That means maximizing different aspects of my physical fitness overall, even if that means a particular aspect might be weaker than if I only focused on that exclusively.

This is called the "interference effect", and it seems like it's increasingly thought to be mostly a non-issue: https://www.strongerbyscience.com/research-spotlight-interfe...