In actuality, the federal pardon will likely affect less than 10,000 individuals but to those people, it means everything. Their conviction is, in effect, erased, so they're able to gain employment, credit, and loans that may have previously been denied to them. Even with a conviction, employers are encouraged to follow EEOC guidance when considering criminal records by using a hiring decision matrix and individual assessments based on the crime and job-relatedness.
See also: Can HR deny employment based on criminal records?
Some governors and gubernatorial candidates agree with Biden, either issuing pardons or promising to, and others hold firm in the "fight against drugs." In actuality, several states classify marijuana as illegal in one way or another but the tide is changing. Many states are decriminalizing or legalizing the drug for medical use or recreational use. This means that simple possession of pot may not appear on background checks going forward in these states. For information on current state laws, review this post which is updated regularly.
If the job requirement includes operating heavy machinery or a high degree of precision, then drug screening is likely part of the hiring process. This qualification will be listed in a background check policy so hiring managers are aware of which jobs require drug testing and which do not. A background check policy will guide employers from drug screening in a discriminatory manner. The background check policy will also include triggers for random drug screening due to reasonable suspicion. In any case, the employer or job candidate will need to provide consent and authorization, just as they would for any other background check.
All in all, marijuana is still considered a Schedule 1 Substance under the Controlled Substances Act. Employers have the right to create a safe workplace for their employees. A background check policy, that includes written clarification on drug testing, is recommended and should be revisited as laws change.