Connectivity Issues Dropped internet

Not sure what to think at this point, built my PC ( nothing special), everything brand new.  I had great internet for about 4 months, now I can barely get the Xfinity speed test to work.  To Xfinitys credit they did warn/tell me that they would be doing maintenance between certain times and internet would be hit and miss.  Now a few more months later, I still have dropped internet all the time, during the day, during Zoom classses.  I have pretty much done everything to stay connected, except have a tech come out to the house, install tech said everything was fine.  

I'm thinking it might be a modem issue, it's the only thing I haven't switched out yet.

Has anyone found a solution? or am I going crazy for nothing

Any advice would be helpful