Recent Data Point. Just returned from a BA TP run, short week end with the wife in Sofia. Managed to secure a fairly good tariff and booked a deluxe room with Cathedral view. I am a Reward Club member but do not hold any status so no particular perks (free internet). Generally I have found the location very good and quite satisfied with the overall experience.
With regards to COVID Restrictions, masks had to be work in all the public area and we were asked for proof of vaccination when visiting for the first time the Floret restaurant for lunch and the Breakfast restaurant. The minibars are empty because of COVID Regulation but no other noticeable difference.
Would I stay again? Probably yes unless I could find a special offer / great tariff at Sofia Hotel Balkan, but just because the location would suit me even better in revisiting the city