[7] He scored his first goal for the 2018–19 season, in a 2–1 home win against Lamia for the Greek Cup, taking advantage of Lucas Boyé's excellent solo effort.

[8] On 24 January 2019, after a year-and-a-half with AEK Athens, Giakoumakis returned briefly to his hometown in Crete to join the island's biggest team, OFI.

[12] On 23 June 2020, Giakoumakis scored his third goal for Górnik Zabrze in the Ekstraklasa, while teammate Stavros Vasilantonopoulos registered his second marker for the club in the same match.

The Greek striker connected with a low pass across the box, neatly turning the ball beyond the goalkeeper into the far right corner, sealing a 3–1 away win against ŁKS Łódź.

[14] On 12 September, in his first game for VVV, Giakoumakis led his new club to win against FC Emmen by scoring a hat trick in the 2020–21 Eredivisie opener.

After a reasonably good start to the competition, the club was unable to win the last fourteen matches in the league and was relegated while Giakoumakis became top scorer of Eredivisie.

On 31 August 2021, the last day of the summer transfer window, he signed for Scottish Premiership club Celtic on a five-year contract for a fee of £2.5 million.

[24] On 22 January 2022, Giakoumakis started for the first time in three months and rewarded Ange Postecoglou with a goal in a 2–1 away win over Alloa Athletic in the fourth round of the Scottish Cup.

[29] On 19 March, he scored his second hat-trick in five games as Celtic beat in-form Ross County 4–0 to move six points clear of Rangers at the top of the table.

[33] His performances that season led to him becoming a popular player amongst the Celtic support, who made a chant in his honour based on German band Nena's single 99 Luftballons.

[42] On 8 November 2023, in Atlanta's 4–2 win over Columbus Crew, the Greek striker became the first player in club history to contribute to three goals in a single MLS Cup Playoffs match.