Earlier this year I upgraded from a 5S to a 14 but before the upgrade started I exported all the data from Apple Health just in case. Also made sure that there was a backup of the 5S on iCloud. There was no need to worry as the moment the new phone logged into iCloud the backup was restored including all the Health data.
Health data that since I bought an Apple Watch 9 has been growing at an asronishing rate. Did a recent export of all the data and it came out as 90Mb!; the export is for me to start planning how to analyse all the stuff in a better way than the one-by-one display of Apple Health on either my iPhone or iPad.
I like to eliminate the possibility of transferring any “cruft”
to a new device. My approach has always been that new
hardware starts fresh, any major sfw versions are installed
on newly formatted media. Minors and patches are incremental.