Blocs has became very slowly

Hello everybody,
After to have made changed the system of my computer (Mac Pro 2008) per “Mojave 10.14.6” and installed a new graphic card (Nvidia GetForce GTX 680, VRAM 2 Go) I have big problems of speed with Blocs 3.4.2. It turns very, very slowly, really. Yet, I haven’t no problem with the other software, InDesign, Photoshop, Premiere, etc. to name just a few among the greediest.
Of course, I installed again the 3.4.2 version after to have cleaned all.
So, if among you someone has known the same, I will be delighted to have his return of experience, mainly if he found the solution.
Thanks by advance and sorry to my very bad English.
Have a nice day,

I am on a Mac Pro mid 2010 with Mojave and an RX560 card. Blocs runs fine here and your computer should have more than enough power to run Blocs. My ancient 2007 iMac was fast enough until it became incompatible recently with El Capitan.

I guess you must be using some kind of patch like Dosdude to run Mojave and I wonder if that is the problem. It’s very hard to know unless you can supply some kind of diagnostic report. Just a thought, but you may be able install the old video card and restart your computer. The display will probably look strange, but if Blocs runs quickly that could point to a graphics related issue.

First, thank you very much for your answer.
For years it is a specialist wy is in charge the maintenance of my computer. He is excellent but there, alas, he is currently on holidays.
I can’t more to the moment using “Blocs”. It is impossible to work, so much it turns slowly. This is a pity because I have to make an urgent site and I am forced to use again Muse.
I am going to transmit your analysis to my specialist when he will back off his holidays.

Have a nice day,
P.S. I tried with all versions de Blocs. The reactions are the same.

@Norm may be able to help. The old Mac Pro is still a great machine but I am very aware that things like this will become more difficult in time with potential performance and compatibility issues. This is why I have not moved to Catalina.