I noticed a similar question posed but several years old in a closed thread.
In that my memory isn’t the sharpest and for many but the simplest of vba functions I have to look up everything over and over I don’t mind delving in to learn a language new to me, but I do have at least one Excel project with well over 10,000 lines of code; it’s situations like this that have prevented me from exploring switching over any further, as much as I would really like to, for the last few years.
LibreOffice can open Excel .xls files with some limited support for the contained VBA code. I doubt it would even be close to handling a VBA project of 10,000 lines.
LibreOffice Basic and VBA are very similar, but the difference between Excel Objects and LibreOffice UNO Objects and structures is what makes the conversion difficult.
I think you should consider some other programming language for your 10,000 line project, perhaps using LibreOffice Calc only as an interface to the user for input and output. I’m working on something similar, trying to use this as an opportunity to restructure the whole project and making very slow progress.
I use LibreOffice for new work, but keep Excel available until no longer needed. It still ties me to Windows but hopefully I can break the tie in a few years.
I suspect your strategy is best. btw, it is at 17,352 lines at this point, though that does include comments…
This idiot project should be in a more database oriented program, but the couple friends who requested it asked it be in Excel because they thought they could better work with it if it were. Yeah; right.