A Study of Obinutuzumab, Rituximab, Polatuzumab Vedotin, and Venetoclax in Relapsed or Refractory Follicular Lymphoma (FL) or Diffuse Large B-Cell Lymphoma (DLBCL)

Participants will receive a fixed dose of obinutuzumab, 1000 milligrams (mg) via intravenous (IV) infusion to be given on Days 1, 8 and 15 of Cycle 1 and on Day 1 of Cycles 2 to 6. Cycle length will be 21 days. For eligible participants, post-induction treatment may be given at a dose of 1000 mg via IV infusion on Day 1 of every other month (starting from Month 2) for up to 24 months, until disease progression or unacceptable toxicity.

Participants will receive a fixed dose of rituximab, 375 milligrams per square meter (mg/m\^2) via IV infusion to be given on Day 1 of Cycles 1 to 6. Cycle length will be 21 days. For eligible participants, post-induction treatment may be given at a dose of 375 mg/m\^2 via IV infusion on Day 1 of every other month (starting from Month 2) for up to 8 months, until disease progression or unacceptable toxicity.

Participants will receive polatuzumab vedotin via IV infusion at doses of 1.4 or 1.8 milligrams per kilogram (mg/kg) (for FL), and 1.8 mg/kg (for DLBCL) on Day 1 of each 21-day cycle for up to 18 weeks during induction treatment. Polatuzumab vedotin will not be given during the post-induction period.

Participants will receive venetoclax film-coated tablets at doses of 200, 400, 600, or 800 mg (for FL), and 400, 600, or 800 mg (for DLBCL) on Days 1 to 21 of each 21-day cycle. Post-induction venetoclax may continue for up to 8 months, until disease progression or unacceptable toxicity.