There's a tag for employees who use ER or the Speak Up portal: #FormerEmployees.
Document everything, and do it loudly.
Example: Your manager excludes you from a leadership offsite. Don't have a pity party in your private journal. Send an email to manager, cc offsite attendees: "As you know, I won't be attending the offsite next month. One of my projects is on the agenda, so I wanted you all to have my input in advance of your meeting." blah blah blah.
Or after a 1:1 meeting where you're criticized for an unfinished project, write "In our 1:1 this morning, you asked about Project X. I reminded you that when I returned from leave after my spouse passed away last spring, the Project X PM was on sabbatical. The PM moved to a different org when they returned. I meant to keep you informed in real time, but we have not met 1:1 since my spouse passed. Let's get those 1:1 meetings back on the calendar so you can be better informed."
Trust no one except yourself.