Activate iCloud for Photos on a MacBook

I have had a MacBook for years. My current one I've had since 2008. Still works great and I backed up everything with Time Machine as this was a time before iCloud. I haven't used this Mac in years. Since then I have mostly used my iPhone and iPad for everything. Recently, my sister gave me her old Mac Book Pro from early 2015. I completely wiped it, setup with my user account, AppleID, etc. I also started it up from my last Time Machine backup. So when I did this it dumped all the photos I had back up at the time on this Mac Book. There is about a 8 year gap from the end of the time machine backup and where my current iCloud photo back up is now on my iPad and iPhone. I want to activate iCloud for Photos on this Mac Book to free up hard drive space. My question is, if I do that, will it make an iCloud backup from the Photos file on the Mac Book is, or is iCloud smart enough to know that the current iCloud from my iPad/iPhone is current? I am worried that it will default to the Photos file on the Mac Book, essentially erasing 8 years of photos I already have in iCloud. Any advice is appreciated.