For 2021 tax returns the official FTA exchange rates are:

USD1   =  CHF 0.9143082CHF 0.911141
EUR1   =  CHF 1.08101082CHF 1.036150
GBP1   =  CHF 1.25746523CHF 1.234099

Official foreign exchange rates as of 31 December 2021 are available here. In this list are also included rates to apply for the main cryptocurrencies (these are found with the list of national currencies). These need to be reported in the tax declaration.

BTC 1 = CHF 43,071.028398
ETH 1 = CHF 3,389.950242