My MacBook Pro is very slow

The most common cause of "slow" in Retina Macbook Pros is the installation of useless third-party utilities that claim to protect, disinfect, clean, or otherwise pamper your Mac. They interfere with elegant automated maintenance and protection routines you paid Apple to build into the operating system. That includes client-side VPNs—those that get hyped in TV adverts.

Do you have any anti-virus/security apps, so-called "cleaning" apps, or other fearware installed?

local store said they won’t check old Macs

True—sadly it's been that way a long time. And we are end users like you who can neither see nor touch your device for evauation. However there is a tool developed by one of our most respected members here that lets us safely and remotely look for issues without our playing a protracted game of "20 Questions" that could go on for days.

We can quickly and within the confines of these forums help you determine what issues are at play if you use EtreCheck Pro, available here:

https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about drive performance, software issues, and RAM usage. EtreCheck was created expressly for displaying information in these forums to help us help you by remotely evaluating Mac issues. It will not reveal any personal or secure information.

The report needs to be posted here where those of us the have read thousands of them can evaluate and recommend action you can take. Please see this excellent user tip on how to post long text reports like EtreCheck's into a forum response:

How to use the Add Text Feature When Post… - Apple Community

As Allan Jones wrote, "The most common cause of "slow" in Retina Macbook Pros is the installation of useless third-party utilities that claim to protect, disinfect, clean, or otherwise pamper your Mac."

The EtreCheck report you posted indicates not only has that Mac been hobbled by "Kaspersky", Apple's own built-in protections have been disabled. That's the polar opposite of what a Mac needs to work reliably. Uninstall the utterly worthless "Kaspersky" product, and re-enable macOS security.

A number of other culprits are evident also, including but not limited to "megaupdater" and other such unhelpful "helpers". Macs don't need that kind of help. Rule 1 of Macs is don't install junk.

Kernel boot arguments - This computer has custom kernel boot arguments.

I do not know what those arguments are intended to accomplish. If you don't either, undo those changes as well.

/etc/hosts - Count: 1 - Corrupt!

The hosts file does not get modified on its own. If you have no knowledge of how that occurred you may want to review Fixing a hacked /etc/hosts file - Apple Community.

Portable Macs also need a working battery. I understand replacement options may be limited, but if the battery indicates it needs service that needs to be addressed.

As far as getting rid of "Kaspersky" goes, regrettably I have to resort to what is going to seem like a "boilerplate" caveat:

• As a rule, I prohibit the installation of such things on my production Macs. Moreover, I don't know how to remove them. When I install them, for evaluation purposes or in an effort to help others fix their problems, I restore a Time Machine backup created prior to those installations. That takes two or three minutes. It is the only certain way to ensure their complete eradication. Of course you must have a TM backup that precedes their installation.
• In addition to determining just how they may affect a Mac's operation, part of that evaluation is determining how effective the product's uninstallation instructions might be. In nearly every case, their uninstallation instructions don't work. At best they work with less than complete effectiveness. "Kaspersky" may be in that category.
• Ironically, some of the worst examples of Mac malware (particularly, "cleaning" apps) have uninstallation instructions that work with surprising effectiveness. "Anti-malware" products would do well to emulate them. Of course it's best to avoid all that garbage to begin with. That's why I say "rule 1 of Macs is don't install junk." It's the first step in a well-worn path to misery.
• In extreme cases I advocate erasing the affected Macs and reconfiguring them from the ground up. I don't think that's justified in your case though, at least not yet. It may be helpful to reinstall "Kaspersky" followed by immediately uninstalling it according to its instructions. That takes us full circle to the first bullet point above.

Does the SSD need a replacement or it's fine?

I really don't think that's justified either at this point.

That report indicates "Kaspersky" remains installed. Your Mac will not work properly until it is removed.

The easiest way to remove the custom kernel boot options is to reset that Mac's NVRAM values to defaults: Reset NVRAM on your Mac - Apple Support. As I wrote I don't know the purpose of those boot arguments nor do I know their effects.

Your drive scores are lower than what I expect to see in that Macbook Pro model:

Performance:

System Load: 2.42 (1 min ago) 3.06 (5 min ago) 3.97 (15 min ago)

Nominal I/O usage: 4.33 MB/s

File system: 21.70 seconds

Write speed: 915 MB/s

Read speed: 1927 MB/s

Typically they should be 1800-2000 Writes and over 2500 Reads.

Useless anti-virus can do that.

In your first report, "SuperHuman" processes are using vast amounts of resources.

Beyond that, there is so much overhead from add-on software that it is hard to know where to start. However, evicting Kaspersky with extreme prejudice is a good place to start.

The US expressed their concerns about Kaspersky in 2022:

https://www.reuters.com/technology/exclusive-us-warned-firms-about-russias-kaspersky-software-day-after-invasion-2022-03-31/

Please determine if the same problems occur in "Safe Mode": Use safe mode on your Mac - Apple Support.