The DoYogaWithMe Youtube channel has a one-hour video on spinal care. It is here at this link. For some reason they have disabled the embedding function.
This physical therapy Youtube channel provides a daily video covering a wide range of subjects with adaptations for fitness/ability level. Here's a recent one with great options for back and core strengthening:
Michele Kenway is a physiotherapist who focuses her suggestions on exercises that are safe for women with pelvic floor issues. They are effective for anybody, though. She has 3 videos that target the back, and they are not difficult at all:
This 14-minute video from The Training Toole Youtube channel is directly focused on osteoporosis exercises for the back:
And there's a video from the Healthy Focus LLC Youtube channel:
that links to an article that provides written instructions for the exercises.
The following 2 videos from the Jessica Valant Pilates Youtube channel are (as is the one directly above) targeted to people who have scoliosis (or a curvature of the spine), although I don't do any of the activities that involve spinal flexion:
The Five Parks Yoga Youtube channel has some videos that I like (though I don't do the cat cow or other poses that require spinal flexion, I don't do shoulder stands, and I modify some of the poses):
Margaret Martin's Youtube channel offers videos demonstrating exercises, and I love this one for back-strengthening specifically for people with osteoporosis:
I do some kind of spine strengthening exercise daily.