The answer appears to be 0.
There's nothing mentioned on the relevant Wikipedia page:
https://en.wikipedia.org/wiki/List_of_D%C3%A1il_by-elections
Further, the official publications which provide details of all elections and bye-election in the Irish Republic don't make any reference to a Dáil Éireann bye-election having taken place since the one for the Dublin Bay South constituency in July 2021:
https://www.oireachtas.ie/en/publications/?q=&date=&term=%2Fie%2Foireachtas%2Fhouse%2Fdail%2F33&fromDate=16%2F12%2F2022&toDate=16%2F12%2F2022&topic%5B%5D=elections