This is a common misunderstanding. In fact, the USD/GBP exchange rate has no effect on the value of 100 shares of VUSA.L after their conversion to EUR.
Suppose GBP depreciated against the USD by 5%, and EUR depreciated against USD by 1%. Then the price of VUSA.L will gain 4% relative to the price of VUSA.DE, and VUSA.DE will gain 1% relative to VUSD.L (the USD-priced equivalent of this fund). Thus 100 shares of VUSA.L or VUSD.L or VUSA.DE can always be sold for the same number of EUR. Such holdings could also be sold for the same number of GBP or same number of USD.
The important thing when buying either version of VUSA is the exchange rate variation between USD and the currency in which you live and pay tax, but it really does not matter whether you buy VUSD.L, VUSA.L or VUSA.DE, except in the cosmetic sense of seeing the value of that basket of S&P 500 companies expressed in $, £ or €, or if you had to pay significant currency exchange fees (which you don’t on T212.)