Re: "How can I fix GarageBand crashing during audio recording on iOS 26?"
Wondering if your iPhone has enough memory / storage space free in which to operate smoothly.
Eg: seems an iPhone needs around 8 Gb free for the everyday tasks. (NB: Any iCloud storage is quite separate.)
As audio in Garagband is memory intensive, the app may require more space than iPhone has available ?. 
If your iPhone is short on space, it is wise to back up iPhone data, before making space available.
If needed: How to check the storage on your iPhone and iPad - Apple Support
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Re: "GarageBand will crash when recording audio on a project, will crash about 3 times without saving the last modifications to the project before it works properly once, it keeps doing that every time no exceptions".
It is a good practice to keep on saving every now and then while creating / modifying any project.
Large, memory-intensive Garageband projects may be best created on a Mac.
Available resource: GarageBand User Guide for iPhone - Apple Support