Bitlocker has just turned itself on

@TeesValleyTech  Dell ships at least some systems with BitLocker "staged" on the Windows partition, meaning that the drive is encrypted but BitLocker is suspended, which means it still behaves like a regular drive.  If you choose to link your Windows logon account to your Microsoft cloud account, then BitLocker is fully enabled on the Windows partition -- which happens instantaneously at that point since now it just has to undo the suspension rather than perform the encryption -- and your Recovery Key is backed up to the cloud in your Microsoft account.  But other drives should NEVER have BitLocker enabled automatically unless maybe your system was subject to some centrally managed server that enforced a policy of some kind, which can include backing up Recovery Keys to that server.  That's possible, but since you're talking about a consumer-oriented Inspiron model, I'm guessing that's not your scenario.  And in fact given that you mention having installed Windows 10 Pro yourself, even that "staging" shouldn't be a factor.  A clean install of Windows from regular Microsoft media to my knowledge does not work the way I described; it's something that Dell does.  I suppose Microsoft may have changed something recently since I haven't clean installed Windows in a while and don't link my Windows account to my Microsoft account anyway, but I'd be surprised.

The only other possibility I can think of for why BitLocker would be enabled even on non-Windows partitions would be malware.