Synology Photos - Photos available offline in full resolution

I use Synology Photos, but hate the loading delay when trying to find certain photos. Is there a way to have all my photos available offline? I often have very bad service so it makes finding photos impossible. I have plenty of storage space on my iphone.

I tried setting cache to ‘no limit’, and then scrolled through my entire collection to load thumbnails but they are too low resolution. I didn’t see a way to load full sized photos into the cache.

Thanks in advance!