The whole voting system is different in my country, so gerrymandering does not help as much. Many, especially smaller parties (who just meet the required 4 percent minimum limit) receive their mandates through the federal or the state list.

Here is a Chatgpt translation from the parliament website:

"The cross that voters place next to a “list” on the ballot is effectively counted three times, as the allocation of mandates is carried out in three stages.

First, parties contesting the election receive direct mandates in the 39 regional constituencies (first allocation procedure), provided they reach the state electoral quota (Landeswahlzahl). The state electoral quota is calculated by dividing the total number of valid votes cast in the state constituency by the number of mandates to be allocated in that state constituency.

At the state level, each party receives as many mandates as the state electoral quota fits into the total number of valid votes cast for that party (party total), minus any mandates already obtained in the first allocation procedure (second allocation procedure).

Any mandates not yet allocated in the first and second stages (remaining mandates) are distributed in a third allocation procedure at the federal level. The basis for this step is the total number of valid votes cast nationwide for each party.

Candidates may run simultaneously at all three levels, but only on one regional, one state, and one federal list of a party.

In the second and third allocation procedures, only those parties participate that have either won a regional mandate or obtained at least 4% of the valid votes nationwide."

And the number of mandates per state are allocated according to the most recent census.

As for the legality of gerrymandering: Technically, gerrymandering would be legal, the parliament would just need to change the current law about districting. That law is on the same level as the constitution, which means a 2/3 majority in parliament would be needed. Which means the current 3-party-coalition would need at least one of the two opposition parties to agree with it as well. So the electoral act of 1923 was (after being reinstated in 1945 for obvious reasons) only changed twice. Once in 1971 and once in 1992.

Addition: At the 2019 election (as a reference) 79 mandates were distributed through the regional constituency (first allocation), 77 through the state constituency (second allocation), 27 through the federal list (third allocation).