One of the ways I have handled this is to have a "check out sheet" that shows where I turned in my key fobs, badges, vpn tokens, etc. to. It was usually signed off by a responsible person in each area. BEFORE I turned it in to the final person I made a copy for my records so that I would have proof that I turned everything in.
Hopefully your place had good policies around this. I do not allow generic accounts where I work except for in very rare cricumstances and have good procedures around them. If someone needs access they should have their own access (not talking about service accounts). If I have to perform an investigation I do not want people to use the "shared" account or shared password excuse.
If you have concerns that someone might use your accounts because it is easier, then ensure you close any loopholes you can. If they are not willing to lock your account, lock it yourself through 3 failed login attempts. Only do this if it would not cause any problems. By doing this you should know that your account was locked at the time of departure. Unless of course if your account has some running process or other business process that it would cause havoc by locking it then don't do it, but then again they shouldn't be running the business this way. They would be able to unlock it of course, but then there should be a log of that happening, which you shouldn't have had access to anymore after you leave.
In the end if they do not terminate your account and someone does continue to use it, there is not much you can do except to ensure that there are no remnants hanging around on your personal devices like an email login, ensure you delete any apps you installed on your phone for MFA/2FA or other business processes. Remove any vpn software used for company business if you had to work from home and used your own equipment (and yes I do realize this does happen). Remove any favorites/bookmarks to company sites from your browsers. If you are still worried then keep good records of your termination/exit process. And I will add this caveat for others as I don't expect you would try this, but DO NOT try to login after you leave to check and see if they have terminated your accounts! I have heard of horror stories of ex-employees that thought they would check up and see if their former company was doing the right things in regards to terminated accounts and then have it go very badly for them when they brought up the failure to terminate their old accounts with their FORMER employer. At that point you are effectively hacking your former employer, which is frowned upon by the courts.
Luckily most places I have worked had a company issued smart id card that was tied to my login. Once I turned that in, I no longer had any access.
