Is it really bad to slightly lie/exaggerate on a job application?

I dont mean lying about your grade or previous jobs, I just mean lying about your previous accomplishments/responsibilities in a previous role.

For example, saying in the job application that you were part of a university society when you weren’t, saying you participated in organising a charity event at a previous job but you didn’t (or had little involvement).

Would you consider these things to really be checked by an employer? I’m just curious as I wouldn’t think they do such specific checks.

Yes. Employers reserve the right to verify information that you put on your application. Some don't bother performing the due diligence whilst others do. Best not to risk it.

I dont mean lying about your grade or previous jobs, I just mean lying about your previous accomplishments/responsibilities in a previous role.

For example, saying in the job application that you were part of a university society when you weren’t, saying you participated in organising a charity event at a previous job but you didn’t (or had little involvement).

Would you consider these things to really be checked by an employer? I’m just curious as I wouldn’t think they do such specific checks.

I would say if you had 0 involvement in something then don't mention it. If you had some, even if it was the smallest bit, yes, exaggerate that to your hearts content there is absolutely no way to quantify the extent of your involvement in something and even if there was, there is no way an employer would go to the extent to check the level of your involvement in organising a charity event for example.