Browser loading speed has slowed since I get TMO Home Internet and don't know why.

In effect I am trying to recommend doing that which is simple and easy first. To trouble shoot performance issues it is necessary to start at the bottom and work up and not jump into more complex pieces of the puzzle. There could be a number of reasons for slow load times for pages. An online search can result in a significant amount of information about this but well that might be slow. :-) 

Depending upon the signal you have for 4G LTE and 5G NR signals it could be a major datapoint to know. If you only get 100 Mb down with an n41 5G LTE secondary signal then it could be in part due to the SNR being poor which can suggest packet loss/damage resulting in poor performance. The n41 5G signal can do much better than 100 Mb down. If there is vendor traffic throttling well this might account for the speed being only where it is. The key though is to know if there is a strong clean signal with low signal to noise ratio. If there is noise the performance will suffer. Working on trying to improve the signal quality to have better SNR would help with performance.

You can try clearing the browsing data say on Chrome and test after doing so. To clear out Chrome browsing data go to Settings  then search for cache. The results for the Security and Privacy window should highlight "cache". You can then use the navigational arrow to the right to use the options to clear browsing data. There are three boxes that will probably be selected in the basic option tab. If you go to advanced you can see additional options. If the slow loading is due to stale cached data then when you clear out the cache and new information is pulled in it may improve the loading. The first time a page is accessed after clearing the cache it will probably load slow but if the issue is related to stale cached information this might help. 

NOTE: Start with only the cached data and if you want limit the time to say one day. If you know you have a site you frequent and want to be selective then limit the time. If this helps consider taking it farther. 

I launched Chrome, which I seldom use now, and when it came up the default startup page rendered a bit slowly for me. I went and cleared the browsing data and then launched a new tab to go to the start page. It did render more quickly. I have seen this before but where all browsers behave the same well not so much. 

If you run a speed test with speedtest.net it should provide up and download values and latency for the communication to the server. The latency value would be good to know. If latency is less than 60 ms that is positive. Jitter less than 10 ms also should be ok. If there is loss what the % is would reflect on performance. 

If there is loss then another important bit of data to look at is in the router web interface. Web into the 192.168.12.1 interface and record the data on the "internet Connection" for the Primary and Secondary signals. If the SNR, signal to noise ratio is poor that would suggest noise so performance would suffer as retransmissions of packets would take place. The result would reflect what you see in browser load times. All the values in this data would be helpful to know to rule out the signal or point to an issue in the cellular signaling. If the problem is not due to the cellular signaling then it would be necessary to back into an investigation of the local wireless or wired connection by the client.