Here's a basic workout I did the first 3 or 4 times back at the pool after they started opening up for me a few weeks ago.

Warm Up
300 warm up
3 x 100 - 50 kick, 50 swim (kick on stomach with snorkel or kick board), with fins
3 x 100 - 50 kick, 50 swim (kick on back, or kick on stomach if you really hate kicking on your back), with fins

Main Set
300 pull easy/moderate (snorkel, buoy)
4 x 100 swim at moderate effort (faster than warmup, slower than "fast")

300 pull easy/moderate (snorkel, buoy)
12 x 25 swim at fast (~90%) effort

Cool Down
200 easy