I purchased an M4 iPad Pro and it arrived today. I went to set it up from my previous iPad Pro but it is running iPadOS 18, and 17.7 is the highest for the M4 currently. I updated on the 17th I think (a day or two after 18 came out) and wondering if I should wipe the new iPad and start again and try using a 17.x backup, or set up as a new device.
If I remember correctly, there is only ever one generation of backup stored in iCloud. Especially in scenarios like yours with different software versions, this is not enough. My recommendation is both still keeping the previous iOS/iPadOS version as long as Apple still supports it during the transition period. And additionally to iCloud backups, do manual backups to a PC or Mac with iTunes/Finder. There you can have multiple backup generations.
I think there were three or four back ups available from my pro. I ended up using the 18.1 beta and then doing a restore. I forgot i can do a back up to my MacBook. I will do one of those tomorrow.