There are 129 seats in the Scottish Parliament at Holyrood. The most recent election to the Scottish Parliament took place on the 6th of May 2021. Following the election, the SNP initially formed a continuing minority government, before entering into cooperation talks with the Greens. That led to the formation of a cooperation agreement between the two parties, with the Greens entering Government with two ministers.
However, unlike a full coalition government, the Greens are not represented in cabinet. Additionally, the two parties have identified areas of disagreement where they may vote separately, and have further stated the deal does not preclude each working with other parties where they consider it appropriate.
The Presiding Officer Alison Johnstone (shown in black) was elected as a Green MSP. By convention, the PO gives up their party status to impartially chair the Scottish Parliament. As such, the PO does not normally cast a vote. They will however do so if parliament is equally split on a given issue.
This follows a long-standing convention of parliamentary chairing in the UK, whereby the chair will vote for more debate where possible, and the status quo otherwise. In practice this means that in the case of a tie, legislation in its early stages will be passed onto later stages, whereas final stage legislation, other motions, and amendments will fall.