16-Inch 2021 Macbook Pro - 16GB Ram - macOS Sequoia 15.1.1 - Help Speeding Up

If you must use Windows as a guest with Parallel's Desktop, keep that Parallel's software update current. There was just an update 20.1.2 for improved compatibility with Sequoia. Do not keep the Parallels Guest on your Mac. Get a fast Crucial 1TB X9 Pro USB-C 3.2 Gen 2 (1050 MB/s) external drive, and configure your Parallels guest on it. In System Settings > General > Time Machine > Options and exclude that external guest drive. Then add that external guest drive to your System Settings > Spotlight > Privacy panel so it is not indexed by Spotlight.

In Parallels configuration, set the CPU & Memory to Automatic so you do not steal too many resources from the 16GB Mac.

The above, combined with removing all of the mentioned and unnecessary third-party software that will slow your Mac down may speed things up measurably. Currently, you are taking a RAM and CPU hit with unnecessary background processes, and both Time Machine and Spotlight running every time you use a Parallel's guest located on your startup drive.

If this computer is used for work I highly recommend performing regular data backups.

You have installed third party apps that claim to protect, clean, etc. CleanMyMac is one such app that may cause problems.

Using a virtual machine slows down performance since system resources such as RAM are shared between two operating systems. If you must use Windows for work, get a Windows computer.

Uninstall Parallels, all cleaning/protection apps, and reinstall the Mac operating system.

EtreCheck is reporting low free space on you drive. That WILL slow your Mac.

Are you using an exrernal monitor?

I normally have 10-15 tabs open on safari for work.

I am finding more and more web pages that are absolute resource hogs, even in Safari.

I can leave some open in a background window and hear the fans in my Macbook Pro ramp up to compensate for heat produced by the increased workload. The computer will also start to slow when this happens.

Use Activity Monitor to check for piggy pages. User Guide:

View information about Mac processes in Activity Monitor - Apple Support

You need to set AM to view "All Resources" go get a full view o the situation.

As I typed this, I ran a quick test on that "piggy page" issue. I opened a product page for a site from which I buy a lot of Mac stuff. It is in a background window in Safari and opened Activity Monitor. Even in background, its CPU usage is massive compared to open active tabs in Apple Discussions, where I keep 11 tabs open:

I have a CPU temp app that shows my CPU temp rose 14°C—now its 17°C—within five minutes of opening that page, and things are slowing

So use Activity Monitor to see if any of you work pages are "over-achieving." Not much you can do about that other the baing aware.

However, you can be cognizant of your work area layout, making sure your Macbook Pro can breathe. Cool air intakes are on the lower edge of each side, and hot air is exhausted through the hinge area in the back. If any are blocked, internal temps can spike and the computer may slow in response.

"Clam-shell" mode (external monitor, lid closed) can be very hard on the Macbook Pro's cooling strategy. Users too commonly block the hinge by placing the computer vertically, hinge side down, to save space. Three of the four edges of the computer case are critical to effective cooling.

And I agree 100% with my wise piscatorial colleague Bob on Clean My Mac. Starting with the year 2000 and the first OSX versions, Apple have included elegant and automated self-maintenance routines in the OS. Cat-like, Macs clean themselves. They do ALL needed cleaning and optimizing, even defragging—and without outside help.

I have seen plenty of EtreCheck reports here showing hard data that removing CMM sped up a Mac. Hower I think crowded storage cold be a significant contributor to your symptoms as well.