My experience has been that companies will either terminate effective immediately with some sort of severance, or they'll give a notice, where you're on the "books" with them as far as employment goes, but you'd surrender all work hardware and your account would be locked out. You're effectively laid off while you find another job. Your severance in that situation is the fact you're still on payroll for however long your severance period would be.

afaik the cold turkey hard stop in large layoffs stems from wanting to avoid retaliation from disgruntled employees. access is terminated immediately to avoid a "going postal" situation. https://en.wikipedia.org/wiki/Going_postal

Unfortuantely this is the reality for most companies in the US. Only in most european countries do they have this courtesy.

In Europe yes. Depending on the country, you get between 1 and 3 months of notice by law.