EtreCheck health check on my Mac - diagnosing if I have anything to worry about?

If you read through the report it is telling you to replace the battery now.

Your SSD is running very slow, to check the health of your macs drive

download and run this app, https://binaryfruit.com/drivedx

there is free trial period.

Your mac has been up for 17 days, why, the mac does benefit from

being shut down and restarted as this clears out caches and will

improve the macs performance.

Your macs drive is running extremely low on free space, if you run

the mac very low in free space you run the risk of it locking up and

becoming unusable. Offload any files you do not need on a daily basis

to an external drive, When you have confirmed they have been successfully

copied over delete them from your mac. Movies, images and music tend to

take up the most room. Macs need at leat 20GBs of free space to perform

their own housekeeping so always aim to have at least that much free

more is better.

There are 25 items in your Login Items, that's just mad.

Do you need all these apps to open when you start your mac up

I doubt it. All that is doing is eating up RAM memory and wasting system resources.

Open System Preferences> Users & Groups> Login Items and delete the ones you do

need opening on startup using the minus button.

The report also notes that there are a number of system modifications running in the

background. Have you installed apps that make modifications to the system.

Not always a good idea, which apps have you installed that make modifications,

it may be worth deleting them.