In September 2020, he joined Serie D side Nocerina on a free transfer.[2][3] Throughout his only season with the club, he scored two goals and contributed six assists in 29 appearances and was voted as the "Best Underage" player that season.[2][4]
On 25 August 2021, Katseris officially joined Serie D club Cavese on a free transfer.[4] After making just six appearances in the first part of the campaign,[2] he joined fellow fourth-tier side Nuova Florida on 3 February 2022.[5][6] He went on to score six goals and one assist in 18 matches for the club.[2]
Catanzaro
Following a successful trial with Serie C side Catanzaro,[7] Katseris officially joined the club on a free transfer on 19 August 2022, signing a three-year professional contract.[8][9] He made his professional debut on 8 October 2022, coming on as a second-half substitute in a 4–0 league win over Fidelis Andria.[10] On 18 December, he scored his first goal for the Italian club, scoring within a minute of kick-off in a league match against Potenza,[7][11] and thus contributing to a 6–1 victory.[11] He scored one goal and three assists in 18 matches during his first season with the club, helping Catanzaro win automatic promotion to the Serie B.[3]
During the first half of the 2023–24 campaign in Serie B, following an injury to Mario Šitum,[7][12] Katseris established himself as a regular starter for Catanzaro, under manager Vincenzo Vivarini;[2][7][12] thanks to his performances, he reportedly attracted interest from various Serie B and Serie A clubs.[13][14]
Lorient
On 23 January 2024, Katseris joined Ligue 1 side Lorient for an undisclosed fee,[15][16] reported to be in the region of €2.4 million, plus €600.000 in add-ons,[17] signing a four-year-and-a-half contract with the French club.[16][17] In the process, he became Lorient's first Greek player.[16][18] He made his debut for Les Merlus five days later, starting in a 3–3 league draw against Le Havre.[19] On 4 February, he scored his first goal for Lorient, netting the winner in a 2–1 league win away at Metz.[20][21] Lorient was relegated to the Ligue 2 at the end of the 2023–24 campaign.[22][23]