Revolut is charging a 0,5% exchange rate for transactions done over the weekend in order to protect the company from currency fluctuations once markets reopen on the following Monday. That is a little and fair fee.
However, I think Revolut should make an exception for the Bulgarian Lev BGN which is a currency under a fixed exchange rate with EUR since more than a decade due to Currency Board policy. The fixed rate is 1 EUR = 1,9558 BGN and it cannot fluctuate because BGN is pegged to the Euro as shown by ECB since more than 10 years: https://www.ecb.europa.eu/stats/exchange/eurofxref/html/eurofxref-graph-bgn.en.html
Revolut should create an exception to the weekend fee for BGN/EUR transactions by appliying no weekend extra charge or a charge of 0%. Charging the extra fee in this special case is unfair since between every Friday and Monday the exchange rate BGN/EUR will never fluctuate!
If an exception is applied Revolut has the potential to boom on the Bulgarian market as well as with the many tourists who visit regularly the country.