Thank you very much for your answer
UsageDD via my home page on Chrome and Firefox show different results: where can the gap come from? what is the most reliable result in your opinion?
Anyway TTBF loading results are bad. The rest is okay. So I have to deduce that my theme is too heavy or that it is a plugin theme or outside the theme that is too heavy.
Either USAGEDD tells me the number of queries, the amount of memory and the TTFB and I have to draw conclusions and find the problem. It does not give any additional track to find the plugin that would be too heavy or the functionality of the theme that would be too heavy for the page (possibly)?
Via this message I can not send you a screenshot?
Also I did some download speed tests:
Test with Pingdom:
110 queries via Firefox / 84 queries via Chrome
Usage DD indicates 66 queries
PageSpeed Insights: 74/100 via Firefox - 70/100 Chrome
Thank you very much for your attention and your explanations.