What can I do to make a verbal offer more secure?

I received a verbal job offer and was informed that...

1. Everyone I interviewed adored me, I was a clear choice, which is really nice and all but...
2. COVID put the company in a position where they cannot extend me a formal offer right now.
3. There is no timeline, but...
4. The internal recruiter I'm working with wants to stay in touch.

This recruiter and company have been INCREDIBLY professional and unexpectedly compassionate during our interviews, and it has been such a drastic difference from what I've come to expect of the hiring process. I trust that the formal offer will come once there's a chance I can on-board in person, but given that my start date is very TBD, does anyone know how I can work on making this verbal offer more secure?

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