Unzipping it is the easy half. What is inside is a folder of files that all point at each other.
A Notion export is one Markdown file per page with a long identifier appended to every filename, plus a CSV for each database. A Confluence space export is one HTML file per page with its attachments beside it. An Obsidian vault is already Markdown, in the folders you made.
All three unzip with the tools already on your machine: double-click on Windows or macOS, `unzip` on a terminal.
Notion writes links against the exact filename it generated, identifier included. Rename the files to something readable and every link between pages stops resolving, which is the single most common way a migration goes wrong.
Confluence links point at its own page ids, and attachments at a download URL that expects you to be signed in. Obsidian uses `[[wikilinks]]`, which only its own app resolves.
Opening a hundred files one at a time to find out what a workspace contained is the wrong shape of work. Merging the export into one document — every page in order, with a table of contents — gives you something readable in one pass, which is usually what an archived export is for.
If the pages have to stay separate files with working links, the rename and the link rewrite have to happen together, from one map of old name to new. Doing them in two passes leaves a folder of documents that all point at names that no longer exist.