Please diagnose my internet problem?

For the first year and a half-that I had this setup, everything was working fine. Lately, however, the internet will randomly get disconnected every couple of hours, streaming services occasionally buffer and zoom calls frequently drop. Everything generally seems to be moving a tad slower than it used to as well. What's the reason for these problems and how do I fix it?

My sixth sense tells me this is all just a result of generally slow internet and that I can fix it by upgrading to a package with more Mbps of speed. However, this doesn't explain why this is only happening now, and I'd rather not pay more monthly without trying other things first.

I'm wondering if maybe it's time to replace the router/modem. Is less than two years enough time for it to degrade like this? Are there any other rebooting / resetting suggestions I can try internally first before going out and buying something?