Season chicken with salt and pepper; coat lightly with flour. Press Sauté; heat oil in Instant Pot, Add chicken in batches; cook about 8 minutes or until browned on both sides. Remove to plate.
Stir in cider, broth and thyme; cook 1 minute, scraping up browned bits from bottom of pot. Return chicken to pot, pressing into liquid.
Secure lid and move pressure release valve to Sealing position. Press Manual; cook at high pressure 6 minutes. When cooking is complete, press Cancel and use quick release.
Add squash and fennel to pot. Secure lid and move pressure release valve to Sealing position. Press Manual; cook at high pressure for 3 minutes.
When cooking is complete, press Cancel and use quick release. Remove chicken and vegetables to platter; cover loosely to keep warm.
Press Sauté; cook sauce about 5 minutes or until slightly thickened and reduced by one third.
Serve sauce with chicken and vegetables; sprinkle with walnuts and basil, if desired.