Rectosigmoid mass. Bulge neoplastic?

My dad had bowel on and off for 6 months. A gastro specialist did colonoscopy and report said a mass in rectosigmoid region 10cm from anal bulge neoplastic? pet ct said luminal narrowing of the colon wall causing dilation of large bowel immedietly we  got the surgery done immedietly and tumour removed tumour biopsy said  all 12 lymph nodes are free t3N0 lvi plus pni plus emvi plus and high budding. Heart ef 40 to 45 percent. My question is that shall we go for ctdna or not and also as per mosiac trial they say that chemo specially oxilaplatin benefit in high risk stage 2 disease is very limited compared to stage 3 disease so shall we skip oxilaplatin and  prefer only s1  or skip chemo totally if ctdna negative Please advise whether to do ct dna or go for chemo directly or omit chemo totally outwieghing the risk of toxicity