It’s a truism, but find something you enjoy. Exercise for the sake of it is boring as hell to many people, which is why they don’t do it.
If you like walking, increase the speed, the amount of time, the frequency, the distance, the terrain - try Nordic walking, or hill/fells walks. Buy some weights to wear while you do your current walks. Join a walking group.
Take up roller or ice skating. Football, netball, tennis, padel, cricket. Trampolining. Cycling - a group near me do fun, off-road, illuminated rides which look great (I can’t make the times they go sadly). Try a couple of parkruns or outdoor boot camps. Go swimming, or even aqua aerobics. Yoga. Pilates. Clubbercise. Dance. Kayaking/canoeing/rowing/paddleboarding.
I’ve had a go at most of those, some stuck, some didn’t, but at 70 I’m still exercising, which in my terms is doing physically active stuff I enjoy, almost every day.