Your Mac model is too new. Yosemite 10.10.5 only supports Macs from mid-2007 to mid-2012 (plus some 2013 Mac Pro models). Newer Macs require their original OS or later.
However, for daily internet use, modern security standards, and access to current software (Zoom, Slack, Adobe Creative Cloud), you should consider upgrading your hardware or moving to a patched version of macOS Catalina or later using tools like OpenCore Legacy Patcher.
