I think you are asking Libreoffice Calc to do something it cannot do.
In LibreOffice Calc, an array is a "a linked range of cells on a spreadsheet containing values" (per Help article Array Functions). There is such a thing as an "Inline Array Constant", but that's for putting values into an array.
IRR() is not an array function, it is a single-valued function which takes an array as an argument.
I think LibreOffice Calc wants to you allocate those 100 (or 100,000) cells with the same value.
You can populate the cells in various ways. I would put the value in the first cell, then give the second cell a formula that read from the first cell with an absolute reference, then fill that second cell down 100 (or 100,000) times to get the array I needed. All I have to change is the value in the first cell, and it gets propagated through the array.
If you really want to type a concise formula to calculate the Internal Rate of Return for 100,000 payments of the same amount, maybe LibreOffice isn't the best tool for the job. It's a spreadsheet. A programming language, like the Python language and the
numpy.irr() function, might work better.