Steps:
- Cell K1 contains the formula, "=$A1"
- Click on K1 and copy with cmd+c
- Select cell L1, and paste with cmd+v

Expected result:
- The formula in L1 should be "=$A1"

Actual result:
- The formula in L1 is "=$B1"

So it appears the use of "$" to denote absolute cell references (e.g. "$A1", "A$1", "$A$1") is not supported. This would be hugely valuable addition, and is currently preventing me moving from Google to Proton Sheets.