2000-2004 - many dems complained about Bush being illegitimate because of Florida.
2004 - Lots of reports of irregularities in Ohio, involving as many as 100K votes
2008-2016 - a large percentage of GOP believes Obama was not American. A certain narcissist rides this racist nonsense to political prominence.
2016-2020 - Dems complain about Russian interference in campaign (not in voting totals, importantly).
So complaining is normal. But what do all these have in common? Concessions by the loser. Every single time.