I agree with BDAqua that RAM seems to be an issue, and that RAM has been added. What is the make of the added RAM?
Most senior contributors here only use RAM from Crucual or OWC in Intel Macs. The cheaper "Value RAM" that is so prevalent from other vendors does not always play well with Macs, even though advertised as being Mac-compatible.
🔶 An incidental finding not related to your current issue:
Drives:
disk0 - Samsung SSD 860 EVO 1TB 1.00 TB (Solid State - TRIM: No)
Internal SATA 6 Gigabit Serial ATA
Your after-market SSD option is wise, and is running right on the nominals:
Performance:
System Load: 1.88 (1 min ago) 2.39 (5 min ago) 1.46 (15 min ago)
Nominal I/O usage: 0.60 MB/s
File system: 17.64 seconds
Write speed: 508 MB/s 👍🏼
Read speed: 529 MB/s 👍🏼
However, TRIMForce is not enabled. What we are seeing is that, at some point, Write speeds in these aftermarket SATA drives starts to decay. It is independent of drive make.
For the OWC Electra SATA 6 SSD in my 2012 Macbook Pro 13", the slow-down took about three years to appear. When it did, the Writes first went to ~250MB/sec (1/2 the Read speed) and continued to drop as low as 60MB/sec, just as slow as the old pokey hard drive the SSD replaced.
With the help of our amazing Grant Bennet-Alder, enabled TRIMForce and then had to do quite a Safe Boots before the Writes returned to normal, but they have stayed on the nominals since.
Information I used to enable TrimForce is here:
https://eshop.macsales.com/blog/31619-how-to-execute-trimforce-command-with-your-owc-ssd/
