I would distinguish election observer groups reporting their first hand observations and politicians making statements. For South America:
Claim fraud:
Argentina
Chile
Costa Rica
Ecuador
El Salvador
Panama
Peru
Uruguay
Seek verification:
Brazil
Bolivia
Colombia
Guatemala
Guyana
Mexico
Paraguay
Support:
Bolivia
Cuba
Nicaragua
You might be able to notice political leanings of the groups. Capitalists not liking an election result doesn’t make it fraudulent. The same claims were made of previous elections and proven false after audit.
All of this is to ignore the 100 year history of U.S-backed coups in Venezuela and trade sanctions. It is hard to take American voices seriously when they claim to advocate for the people of Venezuela while enforcing sanctions that destroy their quality of life.