My mac is very slow after update of mac os cataliana 10.15.5,kinldy let me know what to do ,Thanks

Reboot in Safe mode :

Restart your Mac and press and hold the Shift key when starting up. Release the shift key not until you see the login window.

After login in, reboot normally. Does this solve the problem?

Rebooting in Safe mode can take a long time, (even 10 to 15 minutes) so be patient

I agree with the suggestion already made. If that does not resolve your issue, I suggest that you consider the following: repost and let us know the year and model of your Mac and how much RAM you have installed. Catalina is a heavier user of RAM than the older operating systems. Do you use any Adobe apps which may use a lot of RAM? It is a good idea to regularly shut down the computer as the restart cleans things out. (Doing a Safe start is excellent for this.) I recommend periodically cleaning out the history of your browser(s). This frees up RAM. Having a lot of apps open at the same time can slow down some computers that are light on RAM. Last, if you have any antivirus apps installed, REMOVE them. They are completely unnecessary and will slow down your computer and often cause other problems. If after all this the problem still persists, let us know and other suggestions will be made.