The use of Validity doesn't simply restrict the cell to only accept whole numbers.
Easy workaround: In the Validity dialog box - Define any additional filter (less than or equal - and then insert a very big negative number).
The computer have two separate user accounts, the behaviour is the same for both.
Steps to Reproduce:
1. Select any range - eg. B2:B8
2. Open Validity
3. In the Criteria tab, select Allow = "Whole numbers" and mark "Allow empty cels". Don't touch anything else.
4. Click OK and back to spreadsheet
5. Select any cell in the range B2:B8 - say B2.
6. Enter any whole number, say 5.
Error message "Invalid value" pops up.
Should accept number 5 to be entered
User Profile Reset: No
Build ID: 220.127.116.11-4.fc31
CPU threads: 4; OS: Linux 5.8; UI render: default; VCL: gtk3;
Locale: nb-NO (en_GB.UTF-8); UI-Language: en-US
Sorry, but I don't think it is a bug, it could be a request for enhancement.
Maybe 'not equal' '0'
not tested with linux but same behaviour with below win ver., imho notabug,
in the dialog box you define 'whole numbers' and additional! which 'whole numbers', the standard proposal is 'equal zero', and that works, after the steps from OP you can key in '0',
if you change the definition below 'whole numbers' to e.g. 'valid range' and define 0 as minimum and 5 as maximum you can key in '5', but '6' or '4,5' produce error messages,
with definition of a wider range also numbers like +/-8E307 will be accepted,
this is understandable, comprehensible and sensible behavior,
Version: 18.104.22.168.alpha0+ (x64)
Build ID: 761a672d62df1891b9f4f367a499b220ab2b33fa
CPU threads: 8; OS: Windows 6.1 Service Pack 1 Build 7601; UI render: default; VCL: win
Locale: de-DE (de_DE); UI: en-US