Should I shut off the login item that says Thomas Clement? Do I need that app?

Thomas Clement is the person who signed the app for distribution, and one of the packages associated is the Time Machine editor. If you have found and installed an add-on Time Machine editor app, this would be normal. Leave the startup enabled.

Time Machine is not tied to a modem, and usually connects to either a local hard disk or to a local maybe SSD, or to a hard disk or SSD that’s connected to a device elsewhere on your local network. Time Machine does not send data through your ISP modem, nor across the internet. It’s all local traffic.

When system or storage performance is an issue, those problems can to track back to add-on security apps, add-on VPN client apps, add-on cleaner apps, and similar. Stuff that’s generally not needed, or actively hostile to user privacy in some unfortunate cases.

Too much of printer vendor support is problematic (and some of the well-known brands just aren’t all that good), though there are a few old-line printer vendors still with longer support. Making this all somewhat easier, printers with AirPrint avoid most of the printer driver mess. Some background: Which Printer Should I Buy? - Apple Community

Here is the Mac user guide: macOS User Guide - Apple Support

Apple also has free classes: https://www.apple.com/today/