(Note they do not "support" PHP 7 in version 4 so will need to test if this will work in 7.2. Can't use v3 because that doesn't support PHP 8 [well, it does, but with deprecation errors].)
Given this is a non-bundled addon we are under no obligation to support the same range of PHP versions that Composr core supports, esp older ones the PHP community doesn't support. It just needs the PHP minimum version specifying in the addon_registry hook (requires).
Done, but temporarily leaving this open because OpenSpout has a bunch of developer libraries in their Composer; see if we can get rid of these to reduce file size.
https://github.com/openspout/openspout
(Note they do not "support" PHP 7 in version 4 so will need to test if this will work in 7.2. Can't use v3 because that doesn't support PHP 8 [well, it does, but with deprecation errors].)