The tax on dividends from ETFs is 41% in all cases - it doesn't matter whether DWT is deducted or not
If it is then you get a credit for the tax paid abroad, up to the DTT limit (usually 15%) and can reclaim any over that from the foreign authorities.
As for Degiro, it is not clear to me what DWT the deduct.
For an Irish company, they deducted 25% DWT as I would have expected
I have a French company dividend due shortly, so it will be interesting to see what they deduct - I would expect 12.8% but who knows
It looks like they will deduct 26.5% which is the income tax & social security tax rate for a French resident - as a non-resident, the rate should be 12.8%
They have a web page related to DWT tax
https://www.degiro.ie/tax
They say that the tax can sometimes be deducted before they receive the dividend and sometimes they deduct it. As it depends on the type & source of the income payer and the type and residence of the income receiver, I imagine it is difficult to have the correct amount deducted in all, if not most, cases