A Study to Evaluate Safety, Pharmacokinetics and Anti-Tumor Activity of RO7300490, as Single Agent or in Combination With Atezolizumab in Participants With Advanced Solid Tumors

Inclusion Criteria: * Life expectancy of \>= 12 weeks. * Histologically confirmed diagnosis of locally advanced and/or metastatic solid tumors that are not amenable to standard therapy. * Radiologically measurable disease as defined by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. * Agreement to provide protocol-specific biopsy material. * Adverse Events (AEs) from prior anti-cancer therapy resolved to Grade =\<1. * Adequate performance status and cardiovascular, hematological, liver, renal and coagulation function. * For female participants of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse), use contraceptive measures and refrain from donating eggs. * For male participants: agreement to remain abstinent (refrain from heterosexual intercourse), use contraceptive measures and refrain from donating sperm. Exclusion Criteria: * Known central nervous system (CNS) primary tumors or metastases, including leptomeningeal metastases, unless protocol-specific conditions are met. * Active second invasive malignancy within two years prior to screening. * Significant cardiovascular/cerebrovascular disease within 6 months prior to study treatment start. * Any other diseases, metabolic dysfunction, physical examination finding or clinical laboratory finding that gives reasonable suspicion of a disease or condition that would contraindicate the use of an investigational drug. * Prior allogeneic bone marrow transplantation or prior solid organ transplantation. * Active or history of autoimmune disease. * Known hypersensitivity to any of the components of RO7300490 formulation or to components of atezolizumab formulation. * Pregnancy, lactation or breastfeeding. * Dementia or altered mental status that would prohibit informed consent. * Major surgery or significant traumatic injury within 28 days prior to the first study drug administration (excluding biopsies) or anticipation of the need for major surgery during study treatment. * Treatment with radiotherapy, chemotherapy, hormonal therapy, targeted therapy, immunotherapy or investigational drug concurrent or within 28 days or 5 half-lives of the drug (whichever is shorter) before the first study drug administration.