Online COgnitive Behavioural Therapy for Sleep and Mental Health for Older Adults With Insomnia and Subjective Cognitive Complaints

The goal of this randomized controlled clinical trial is to assess a novel cognitive-behavioral program for sleep and mental health using a multidomain web platform (eCBTi+) in participants with insomnia and subjective cognitive complaint. The main questions it aims to answer are: * Whether the eCBTi+ intervention improves sleep (subjective: Insomnia severity index \[ISI\], objective: EEG-based sleep efficiency) sleep and mental health (Geriatric Anxiety Index \[GAI\] and Geriatric Depression Scale \[GDS\]) compared to the control intervention * Whether the eCBTi+ intervention improves cognitive abilities (subjective: Cognitive Failure Questionnaire \[CFQ\], objective: CANTAB executive functions composite score) compared to the control intervention

Participants with insomnia disorder will complete: * A phone interview * Two video conferences (assessment of eligibility and tutorial to set up sleep monitoring devices) * 9 nights of at-home polysomnography with an EEG headband (3 times x 3 nights) * 42 sleep diaries (3 times x 14 days) * 42 days wearing an actigraphy device (3 times x 14 days) * Online questionnaires * Phone call for a check-in with a psychologist * 3 cognitive testing sessions * 10 modules of online information on health, over the course of 10 weeks * In MRI subgroup: 2 in-person testing Good sleeper participants will complete: * A phone interview * Two video conferences (assessment of eligibility and tutorial to set up sleep monitoring devices) * 3 nights of at-home polysomnography with an EEG headband * 14 sleep diaries * 14 days wearing an actigraphy device * Online questionnaires * 1 cognitive testing session * 1 in person session for MRI. In addition, researchers will compare outcomes from participants with insomnia and subjective cognitive complaint to a group of good sleepers to have normative values for imaging data.