my iMac 21,5 late 2013 is slow

Perhaps the storage drive may be full of user-created clutter, to include saved documents, etc.

Too full content, can cause the system to run slower; it needs at least 30% free unused capacity

to be able to function. The spin-rate of the HDD is also cause of mechanical slowness.

Also some of these may have a 'two-in-one storage drive' comprised of a small SSD and larger

HDD. Usually seen by the Mac OS as one, sometimes that gets 'broken' & then two are seen as

separate desktop icons and in the file systems, too.

• How to fix a split Fusion Drive - Apple Support

/support.apple.com/en-us/HT207584

"These steps permanently delete all data stored on the drives that make up

your Fusion Drive. Make sure that you have a backup before continuing." 

This duality ^ is referred to as a 'Fusion' Drive.

• How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an 'EtreCheck' Report - Apple Community

//discussions.apple.com/docs/DOC-250000211

• EtreCheck from etresoft

https://etrecheck.com/about

To show other users who may have some ideas what your Mac is doing; you may get and

use a free running utility called EtreCheck; this allows one to post the generated report in

your Apple communities discussion. ~ Instructions make use of a Text feature, so it all fits.

• How to use Safe mode on your Mac - Apple Support

//support.apple.com/en-us/HT201262

Had you tried to restart in Safe mode? Sometimes temporary file glitches

can be resolved from this; in its simplist form; start in Safe mode, let it run;

and then about 20+ minutes later, restart; then it can exit Safe mode.