It's interesting to consider that most tech companies implicitly allow their employees to invest their own cash, because the cash/equity split is a negotiated term in comp packages.
Also explicitly. I recently interviewed for a new job. Recruiters at both Amazon and Google encouraged me to invest my 401(k) contributions in the company stock. The Google recruiter even had the audacity to (falsely — 2008, 2014) claim that Google had "never had a down year."
Those are public companies; you can do basically whatever you want with their stock, as can anyone in the investing public, because they're subject to stringent audited disclosure rules. What's interesting are the private companies that allow employees to allocate capital to company equity.
Oh, sure.
Having worked at Google until 2019, I do not recall their stock being available in the 401k, nor any direct stocks there. All things available were the boring broad Vanguard funds.
Might have been Amazon with the 401k, and the Googler told me to never sell my RSUs.