The main purpose of this study is to determine the safety, tolerability, pharmacokinetics
(PK), immunogenicity and (if observed) the maximum tolerated dose (MTD) of M6223 as a single
agent (Part 1A) and of M6223 combined with bintrafusp alfa [Part 1B, for both the every 2
weeks (Q2W) regimen and the every 3 weeks (Q3W) regimen] in participants with metastatic or
locally advanced solid unresectable tumors.