When trying to patch, it says "Reversed (or previously applied) patch detected!" (IR3 has been downloaded from this website). Any option I pick from there causes the "1 out of 1 hunk FAILED" message to appear. Then, Factorio itself doesn't recognize the mod as 2.0 proper and refuses to enable it. Using "--keep" command is irrelevant.

What Factorio returns after attempting to turn on the mod:

"Failed to load mods: IndustrialRevolution3/code/gui/gui.lua:33: attempt to index field 'filter_group_button_tab' (a nil value)
stack traceback:
IndustrialRevolution3/code/gui/gui.lua:33: in main chunk
[C]: in function 'require'
IndustrialRevolution3/data.lua:79: in main chunk"

If you can't get the patcher to work, you'll need to edit the mod and delete the offending line. The code should look like this near Line 33:

if data.raw["gui-style"]["default"]["filter_group_tab"] then
        data.raw["gui-style"]["default"]["filter_group_tab"].minimal_width = 48
        data.raw["gui-style"]["default"]["filter_group_tab"].height = 64
        local bx = 52
        local by = 52
        local spacing = 24
        data.raw["utility-constants"]["default"].select_group_row_count = 8
    data.raw["utility-constants"]["default"].select_slot_row_count = DIR.slot_row_count or 10
    -- data.raw["utility-constants"]["default"].inventory_width = 12
end

EDIT: You may have more success with the WSL method. If that doesn't work, I can only suspect that some file is not downloaded correctly.

Apart from that, I have no idea why the patching is inconsistent for some users, sorry.

It did work, thank you. Hopefully anyone who'd encounter an issue like mine would be able to deal with it this way, too.