Four months ago I exported all photos from Google Photos to import into immich, and scheduled followon Takeout runs every two months. I had naively assumed the subsequent exports would be incremental changes from the first one, but they are instead complete exports again. Two months later, download of the first scheduled Takeout repeatedly failed until Google disabled the download links, leaving me unable to download my photos at all.
After another two months, I made another attempt with the next scheduled export. I tried downloading the first archive using Chrome, and it failed twice. I switched to Firefox to download instead of Chrome, and it worked much better. Firefox appears to not give up so quickly and keeps trying. I was able to download all fifteen ZIP archives, fifty Gigabytes each, with only one download failure where I had to start it again.
Hurray!