As the paper you link to suggests, Sweden was involved in the conflict in the late 1970s through (1) arms sales to Indonesia and (2) supporting Timorese self-determination. It's also involved in the eventual independence of Timor Leste decades later, both bilaterally and through its participation in the United Nations, but those politics fall somewhat outside the 20-year rule. Indonesia exported arms to the tune of 21 million crowns in 1980, a number which grew over the decade (again, the paper you link to provides a good summary of all this.)

The Wikipedia article's mention of Sweden supporting Indonesia the way China, the USSR and Cuba are is really shoddily justified - the footnote points to a source called Indonesia (1977), and said publication seems to be a paper produced by the Indonesian foreign ministry. Quite the dead end given these papers aren't easily accessible, and the Wikipedia footnote seems this was a report produced by correspondent Jill Jolliffe, an investigate journalist who worked on Lusophone colonies in Southeast Asia and Indonesia, hardly someone you'd expect to work for the foreign ministry. I suspect the Sweden connection Wikipedia suggest is bunk. Unfortunately the Sweden reference here will probably stay up, there are plenty of gripes people have had when it comes to trying to edit out inaccessible references and perhaps Wikipedia editors here have their own quixotic standards regarding what counts as involvement (although Indonesia's list of arms suppliers, and allies by proxy, will look much longer if this is the case).

The more interesting story here is probably one to do with the tensions Sweden faced regarding the ‘human rights’ issue in its foreign relations with Indonesia. Lying outside NATO, Sweden’s foreign relations during the Cold War often departed from the fiercely anti-communist stance that many other Western democracies maintained within their foreign policy, a stance that provided significant diplomatic leeway and large amounts of aid for Suharto’s regime in the region. (We can also note Sweden’s opposition to American involvement, as /u/Ran4 notes in a comment here sometime ago). High-level foreign officials in Sweden expressed significant concern after reading the 1977 Dunn Report on East Timor, penned by a former diplomat and military intelligence official from Australia who had been present in Portuguese Timor. Claims of a death toll of 100,000, cited by the report as credible were given media attention – notably in the Netherlands and France, but also in Sweden. (Australian diplomats under the Fraser government would actively lobby to suppress the publication and credibility of the report.) Sweden did not completely halt arms sales to Indonesia, even as it remained vocal in the United Nations for Timorese self-determination and against Indonesian intervention and occupation.

Swedish civil society maintained links to international activist networks, of which Amnesty International’s report in the 1980s are most well-known. There is a particularly intriguing Swedish publication by Björn Larsson which I’ve not been able to access (it’s quoted in the Webster article). Titled Det Grymma Spelet: Sverige’s roll i Indonesiens folkmord i Osttimor 1975–1985 [The gruesome game: Sweden’s role in Indonesia’s genocide in East Timor] It was among a number of reports that mobilized people around the world for solidarity with Timor through vivid descriptions of human rights abuses, images of the Timorese people intended to humanize, and providing links to elements of the Timorese resistance like Freitlin. These would have further pressed the Swedish government to adhere to its own control requirements on arms sales, such as a 1983 parliamentary decision intended to prevent export of ‘offensive’ war material, and even re-examine these policies – how weapons were actually used on the field, rather than any abstract technical specifications, determined whether these would have been used against civilians or indiscriminately. Bofors in particular came under scrutiny for illegal shipments that violated Swedish reports, although I note that these arms control debates lie outside the period of the invasion proper.

Further references:

Job, Peter. “The Evolving Narrative of Denial: The Fraser Government and the Timorese Genocide, 1975–1980.” Critical Asian Studies, vol. 50, no. 3, Routledge, July 2018, pp. 442–66.

Webster, David, et al. “Putting Timor on the Global Agenda in 1985: Solidarity Activism Ten Years after Indonesia’s Invasion of East Timor.” Indonesia, no. 107, [Cornell University Press, Southeast Asia Program Publications at Cornell University], 2019, pp. 3–18.