meaning - "Enter information about your education history from secondary level onwards": Is the word "onwards" inclusive or exclusive?

The word onwards doesn't do very much here. Without it,

... from secondary level.

means start at secondary level (include it) and work forward from there. If secondary level were not required, from would be replaced with after.

The only possible reason for including onwards would be to distinguish the requirement from

... backwards from secondary level.

but even that still includes secondary-level education. From is inclusive.

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