A new production release of UCSF Chimera (version 1.17) is available: https://www.rbvi.ucsf.edu/chimera/download.html
Updating to 1.17 is required to continue to use the following tools: BLAST protein, Modeller comparative and loop modeling, and multiple sequence alignment with Clustal Omega and MUSCLE. Due to imminent changes in web services, these tools will soon stop working in older versions of Chimera. Version 1.17 can also fetch UniProt sequences (previously broken by UniProt website changes).
Alternatively or in addition, you may want to consider switching to UCSF ChimeraX instead, as it also has tools to run these web services, as well as many new features and enhancements. https://www.rbvi.ucsf.edu/chimerax/index.html.