When reporting a bug/issue:

• Screenshot:

  >>> fontforge.font().bitmapSizes = (16, 32, 64, 128)
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  SystemError: new style getargs format but argument is not a tuple
  

• The FontForge version and the operating system you're using: 8ce3216 on sid (originally found on 1:20201107~dfsg-4 (bullseye), reproduces on 1:20220308~dfsg-1 (sid))
• The behavior you expect to see, and the actual behavior: as per spec: to be able to assign a tuple there, and actually I'm not
• Steps to reproduce the behavior: see p. 1

To ensure I wasn't holding it wrong I also did:

>>> fontforge.open('Untitled1.sfdir').bitmapSizes
(16, 32, 64, 128)
>>> fontforge.font().bitmapSizes = (16, 32, 64, 128)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: new style getargs format but argument is not a tuple
>>> fontforge.font().bitmapSizes = fontforge.open('Untitled1.sfdir').bitmapSizes
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: new style getargs format but argument is not a tuple

so idk.

What may be relevant and what the template doesn't ask for is the Python version: 3.10.6-1 and 3.9.2-3