https://about.gitlab.com/handbook/being-a-public-company/
Even GitHub was never in a position to go public, that seems to be mere postering to drive valuation or attract M&A offers.
I don't know how much control their external board members have, but if an offer came in, the board may be able to force acceptance instead of going public.
https://about.gitlab.com/handbook/being-a-public-company/