Cash and cash equivalents - Schedule of Cash And Cash Equivalents (Detail) - EUR (€) € in Thousands  | 
Jun. 30, 2022  | 
Dec. 31, 2021  | 
Jun. 30, 2021  | 
Dec. 31, 2020  | 
Dec. 31, 2019  | 
Dec. 31, 2018  | 
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| Schedule of Cash and cash equivalents [Abstract] | ||||||
| Cash at bank | € 24,652 | € 8,274 | ||||
| Total | € 29,775 | € 24,652 | € 6,010 | € 8,274 | € 21,277 | € 1,211 | 
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- Definition Cash at bank. No definition available. 
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- Definition Schedule of Cash and cash equivalents. No definition available. 
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- Definition The amount of cash on hand and demand deposits, along with short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value. [Refer: Cash; Cash equivalents] Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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