You're allowed to need some space. You may feel better if you say so, rather than ghosting.
Something like:
"Sorry I've been ignoring our friendship, I've needed some space. I want to still be your friend, long term, in honor of what we've shared. I might still be quiet for awhile, but I'm okay and I appreciate you."
Friendships can go quiet for years and still be friendships, if both people don't mind.
I understand the distrust for Proton, but I can't help but notice that this could be a huge upgrade for folks fleeing from Microsoft and Google suites.
Edit: But for anyone who wants to conference call with a clean conscience, check out Matrix.org.
Did you try being born ultra rich? I've heard it helps. I wish someone told me sooner.