The usual workarounds
You can share each calendar’s free/busy with the other account, but sharing outside an organization depends on what each employer’s admins allow, and it shows availability to people who look you up rather than adding blocks to the calendar they book against. Copying events across by hand works until you forget one. Automations such as Power Automate tend to duplicate events or miss changes and deletions.
How Kelbra handles it
Connect both Microsoft accounts to Kelbra and turn on Busy only for each. Every meeting on one calendar appears on the other as a plain "Busy" block with the real start and end time, and no title, description, location or attendees. Move a meeting and its Busy block moves with it; delete it and the block goes. Busy only applies to events that started on that calendar, so a copy is never sent back as "Busy" over the real meeting.
Setting this up
Check each employer’s policy on connecting third-party apps to your work account. Some Microsoft 365 organizations require an admin to approve the app first; Kelbra tells you if a connection is blocked for that reason.
Connect your first job’s Microsoft account in Kelbra and pick the calendar people book you on.
Connect your second job’s account the same way.
Turn on Busy only for both connections, so only the time of each meeting crosses over.
Test it: create a meeting on one calendar, check a "Busy" block appears on the other, then move the meeting and check the block follows.
Questions
Will my other employer see my meeting titles?
No, not with Busy only on. The copy on the other calendar is titled "Busy" and has no description, location or attendees. Only the start and end time cross over.
What happens if I move or cancel a meeting?
The Busy block moves or disappears to match. If the same meeting is changed on both calendars at once, Kelbra pauses it and asks you which version to keep instead of overwriting either.
Do I need IT approval?
It depends on each organization. Some let you connect apps yourself; others require an admin to approve third-party apps first. Check your workplace’s policy before connecting a managed account.
Does this work with a Google or iCloud calendar too?
Yes. The same Busy only setting works across Google, Microsoft, iCloud and other CalDAV calendars, in any combination.