Please help us help you and fill where relevant:
LimeSurvey version: LimeSurvey Community Edition Version 6.8.1+241120
Own server or LimeSurvey Cloud: Own server
Survey theme/template: Fruity
==================Dear,I have a peculiar problem. One particular kind of button does not work since some time ago (I don’t know since when exactly). It is the button that is placed below the list of the surveys, or below the list of participants, below the list of responses, and similar.When I mark some entries above (e.g., surveys, responses, participants), the button just remains inactive. So, for instance, I cannot mark a set of surveys and archive them together. It is the only inactive button that I have noticed.We use LimeSurvey Community Edition Version 6.8.1+241120 on our server.I would appreciate some help.Thanks! 

Works as expected here for the same version.

Here some things you can try:

1. Clear your browser cache
2. Open Limesurvey in an incognito window of your browser.
3. Open Limesurvey with a different browser
4. Clear Limesurvey's asset cache
5. Try on a different computer
6. Check any browser plugins that might have an impact on the functionality of websites (e.g. ad / script blockers, etc).