Kindly refer to the following link(s):
Fidya (Expiation for those who missed fasting due to chronic illness) | Sheikh Assim Al Hakeem
A complete explanation about Fidya (expiation) for those who cannot fast
Skipped fasting due to negligence, now chronically ill, cannot fast, can I give Fidya
Are those who have Gastro or Diabetes exempted from fasting in Ramadan?