Mod force researches everything when it should only research the technologies of the kit selected.

Seems like in control.lua around line 750, in this section:
-- Unlock technologies
if kit["technologies"] ~= nil and kitTechnologiesSetting == true then
player.force.research_all_technologies()
--for k,v in pairs(kit["technologies"]) do
--player.print("Technology = " .. technologies[v[1]])
--player.force.technologies[v[1]].researched = true
--end
end

It's commented out to research only required from kit.

Yes, I know about that. Trying some solutions, need some more time...

ChatGPT says that the problem is the print, you're calling technologies[v[1]] but "technologies" is not a table with tech names as keys, instead you can use something like:

-- Unlock technologies
if kit["technologies"] ~= nil and kitTechnologiesSetting == true then
for _, v in pairs(kit["technologies"]) do
-- Print the technology name directly
player.print("Technology = " .. v[1])
-- Set the technology as researched
player.force.technologies[v[1]].researched = true
end
end

and that would probably fix it

Unfortunately, I tried and tried and tried and your advice works fine for huge and big but not for custom kit (around line 917). When choosing custom kit nothing is researched using code you provided. So for custom kit is all or nothing researched, for now. I will keep trying, but now I enjoying much more playing new fabulous DLC. Many thanks anyway!