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Well, this toot is about indicating the used server software.
Using /api/v1/instance it will provide a field [version] (for example "3.5.3"), but no field is provided, that informs about the used server software. Same for a Pixelfed instance (e.g. [version] = "2.7.2 (compatible; Pixelfed 0.11.3)" (example for non Mastodon).
#Mastodon is providing via /nodeinfo/2.0 two fields: [software][name] and [software][version], e.g. "mastodon" and "3.5.3". (Also included supported protocols...)