Transitioning from running to cycling

Now that I’m in my 40’s, I wanted to supplement my running with cycling but I noticed that despite my fitness from running I really seem to be struggling generating power. I started on Zwift pretty regularly this fall. I’ve seen some pretty large gains in my FTP, but it’s not really what I would have expected based on my running fitness. Anyone else make the transition from running to cycling and seem to struggle with it? I can ride at lower watts for quite a long time, but I get pretty wrecked if I try and keep up with other cyclists in group rides or races.