Bulgarian, French and some other foreign pro-Russian politicians indeed visited Crimea during voting for amendments to Russian Constitution. However, they cannot be quoted as experts in elections observation, since observation is a professional activity carried out by international organisations according to common standards.
Contrary to the claim, the European Parliament deputies cited in the report did not "observe" the vote in any sense pertaining to international election monitoring, given that the voting procedure featured no actual foreign observers. For instance, the OSCE ODIHR mission was not invited to monitor Russia’s voting on constitutional amendments. It did, however, see a number of so-called "international experts" who were invited to witness the vote and make gushing statements to pro-Kremlin media about its supposed transparency. A number of these "experts" have documented track records of legitimising sham elections in Russia and elsewhere.
The “Golos” movement conducted an independent observation of the all-Russian vote on the amendment of the Constitution throughout the entire campaign period, from March 2020, including the period of the passing of the normative-legal articles that regulate the conduct of the vote, the initial launching of the processes, their application in relation to the Coronavirus pandemic, the updating of the processes and of course, the days of voting themselves. The long-term and short-term observations were conducted in 42 regions of the country.