After installing macbook pro become so sluggish what to do ?

At this point I suggest that you run an EtreCheck report, and optionally, post it here if you need assistance with interpreting its results.

• https://discussions.apple.com/docs/DOC-250000632

I had a similar experience.

I installed the update and immediately my 21.5" (late 2013) iMac became unusable (beach balling on every mouse click; my Time Machine backup disk showed NO backups had been made; EtreCheck showed MAJOR issues; etc., etc.)

I spent several hours running Apple H/W diagnostics, booted into Recovery Mode and ran Disk Utility on both my Macintosh HD and Time Machine backup disks;. No H/W errors or disk errors were reported.

I then used Recovery Mode to reinstall my last Time Machine backup image just before I installed the last Security Update, and now everything is operating normally again.

I have NO third party S/W installed on my iMac -- I have no idea why this particular update "bricked" my system.

I am sorry to tell you that having only 4 GB of RAM is really insufficient. Today, the minimum amount of RAM for most operating systems is listed as 16 GB.