The only problem I am having though is that it is making me rechoose the disk
We already explained that the "path" to reach the Time Capsule that was used to back up on your old network has changed, so you need to set up a new "path" so Time Machine will know how to reach the Time Capsule backup disk.
If it was going to the same backup image it would know it was already encrypted.
If Time Machine needs to know "where" the Time Capsule disk is on your new network......(it does)......it obviously has no way of knowing now whether the previous backups were encrypted or not......because it cannot even "see" the disk and backups yet.
If all goes well.......after what may be a long time of "Preparing".......Time Machine will discover the existing backup file and continue to back up to that file. The fact that you are using encryption will usually slow things down by a factor of 3-4 times. So, you might see "Preparing for 6, 8, 10 hours or more before the new backup actually begins.
As I noted above, worst case........(this often occurs with users who are using the Catalina operating system on their Macs).......Time Machine will not be able to continue backing up to the existing backup file and it will start a complete new backup again and then move forward from there.
If you are looking for guarantees that Time Machine will back up to the existing backup file, I cannot provide them. Perhaps you should wait for another user to reply who might be able to tell you what you want to hear. I don't know how they could possibly guarantee that their "method" will do what you want though.