First of all if your Mac originally had 8GB of RAM, then you should have mentioned this to Apple so they could investigate the issue. Perhaps you ordered an 8GB model, but only received a 4GB model, or perhaps the repair shop made a mistake and installed the wrong part. If you had an unauthorized repair shop work on the laptop, then it would not be surprising they installed a Logic Board with less memory since finding a used Logic Board with 8GB or RAM may be a bit more difficult.
BitTorrent apps can slow down a system so that would be the first thing I would check and uninstall. I would also make sure all the third party apps are completely up to date especially the Paragon software. The "Native Access" app also had six crashes so you may want to update it or even uninstall it.
I've seen other more knowledgeable contributors on these forums mention that file syncing apps tend to cause extreme system slowness as well, but I don't know if One Drive is one of those or not.
I also suggest running Disk Utility First Aid on the hidden Container. You will need to click on "View" within Disk Utility and select "Show All Devices" so that the hidden Container appears on the left pane of Disk Utility. Even if First Aid says everything is "Ok" click "Show Details" and manually scroll back through the report to look for any unfixed errors. If there are any unfixed errors listed, then you will need to erase the whole physical SSD before restoring from a backup or clone.
You should always have frequent and regular backups. FYI, it is impossible to recover accidentally deleted data from an SSD after the Trash has been emptied plus an SSD can fail at any time without any warning signs.
