Last time I was there was probably 6-8 years ago. I went on one hike led by the parks dept. It was a vertical hike from Riomaggiore up to a sanctuary.
It pegged my heart rate. I’m good walking 10 even 20k steps when traveling. But the climb gets me.
Besides the cardio challenge, you’re walking up and down uneven rocks. So you have to be vigilant about slipping or even getting your feet caught in some crevice.
Even if you don’t have an injury, it will tax your knees and back and in many ways, hiking down will put more stress on your joints, especially if you’re feeling a bit of fatigue from the climb.
The easiest hike is Lovers Lane from Riomaggiore to Manarola, which is pretty level along the coast. It’s very scenic but it’s been closed for about 10 years due to mudslides.
They’re saying it will re-open this July.
https://www.cinqueterre.eu.com/en/cinque-terre-via-dell-amore
But they were suppose to re-open several times during the past 6-7 years.
Otherwise most of the hikes have some climbing elements.
More flat hikes are available in other towns but outside of the CT villages. For instance you can take a train up to Santa Margherita Ligure and walk to Portofino, very scenic and flat.
Portovenere, reached by ferry, is not as steep as the CT villages. You can walk around the waterfront as well as a rocca (old fort) over the town. Again great scenery.