The definition under article 3(21) does not provide a list of services that could be considered as ICT services.  The definition mentions that the services must be provided "through ICT systems" but it is not clear whether those systems must be operated by the same entity that provides the software.  The phrase "on an ongoing basis" is also not clear: would a software licensing agreement be considered to be "on an ongoing basis".  The mention of hardware services (including technical support via software updates) perhaps provides a useful analogy - is the licensing of on prem software (including updates and technical support) equivalent?

Recital 63 mentions "providers of...software" as being included in a wide range of ICT TPPs, but is that just SaaS software providers of licensors of on prem software too?

The ESAs Report on the landscape of ICT third-party providers in the EU mentions "software and application services (IT development; off the shelf software packages, licensing, and installation thereof etc)" as one of the seven ICT service categories.  This seems to be the most definitive expansion on the definition to date but an authoritative Q&A answer to this question would be welcomed to aid preparation ahead of DORA's effective date.