what could be preventing my transaction log autogrowth to be set to UNLIMITED? I have been trying to set the autogrowth of one of my databases to unlimited but despite whatever I do it remains the same.

First thing I have checked if something is holding any locks to my database:

select radhe='kill ' + cast(DTL.request_session_id as varchar(3))
      ,DTL.request_session_id
      ,DTL.resource_type
      ,DTL.request_type
      ,DTL.request_status
      ,DEST.TEXT
      , SP.spid
      , SP.blocked
      , SP.status
      , SP.loginame 
from sys.dm_tran_locks DTL
INNER JOIN sys.sysprocesses SP  
       ON DTL.request_session_id = SP.spid   
   --INNER JOIN sys.[dm_exec_requests] AS SDER ON SP.[spid] = [SDER].[session_id] 
   CROSS APPLY sys.dm_exec_sql_text(SP.sql_handle) AS DEST  
where 1=1
  and resource_type = 'database' 
  and resource_database_id = db_id('junofinance')
  and request_type = 'LOCK' 
  and request_status = 'GRANT'


but there was nothing holding any database locks.
so I went ahead and ran the following:

use master
ALTER DATABASE [JUNOFinance] 
MODIFY FILE ( NAME = N'JUNOFinance_log', MAXSIZE = UNLIMITED)
GO


when I check about the log reuse I get the following:

select log_reuse_wait_desc, * from sys.databases
where name = 'junofinance'




but that is not the problem, as after I few times trying these scripts I got:


then when I check the log maxsize I still get it limited:

exec sp_helpdb 'junofinance'




I have even tried some silly things like disabling the autogrowth and setting it to UNLIMITED

USE [master]
GO

GO
ALTER DATABASE [JUNOFinance] MODIFY FILE ( NAME = N'JUNOFinance_log', MAXSIZE = UNLIMITED, FILEGROWTH = 0)
GO


then it worked fine, go figure!

but then when I re-enabled it, it went back to the limitation:

USE [master]
GO

GO
ALTER DATABASE [JUNOFinance] MODIFY FILE ( NAME = N'JUNOFinance_log', FILEGROWTH = 10240KB )
GO




On this server in particular, I cannot upgrade it, so we are on:


  Microsoft SQL Server 2016 (SP2-CU7) (KB4495256) - 13.0.5337.0 (X64)
  May 16 2019 02:24:21   Copyright (c) Microsoft Corporation  Enterprise
  Edition:  Core-based Licensing (64-bit) on Windows Server 2012 R2
  Datacenter 6.3  (Build 9600: ) (Hypervisor)
If you open BOL article sys.database_files (Transact-SQL)

you'll find that
268435456 = Log file will grow to a maximum size of 2 TB

2 Tb is the max size of SQL Server database log file, if you need it more than 2Tb you add the second log file.

Here you can find Maximum Capacity Specifications for SQL Server that states that 2Tb is the maximum log file size: