In nearly most cases, there are no tax consequences. Donations are gifts and as such are not taxed and in most cases there is no obligation to report them. Always check with the tax authorities in the country of declaration for the exact rules and conditions.
Further information: Government Digital Service
Anyone can receive a donation/gift without having to report it to the tax authorities provided the donation amount does not exceed € 2,418 (this is the threshold for 2023 - the threshold was € 2,274 in 2022). This amount applies PER DONATOR and PER YEAR. This means that you can receive up to € 2,418 per year tax-free from different people - PER PERSON. So you can safely raise €100,000 for example with crowdfunding, without paying gift tax on it, as long as the individual donations stay below €2,418 per donor.
Parents may even gift €6,035 tax free to their child in 2023. By 'child' we also mean a foster child or a stepchild.
More information: Belastingdienst (1) en Belastingdienst (2)
An indirect donation by bank transfer is a purely banking transaction whereby the donor transfers money from his bank account directly to the beneficiary's bank account. Donations by transfer are not subject to any registration requirement and therefore do not have to pay any gift tax.
More information: Federale Overheidsdienst Financiën (FOD)
If you collect money as a private person (§ 7 ErbStG), the tax-free amount of a donation for this purpose is € 20,000 (§ 16 ErbStG) per person within a period of 10 years, after which gift tax applies. This tax-free amount can be higher in case of a family tie between the donor and the recipient, depending on the degree of kinship.
If the same person makes several donations, they are added together. However, donations are not fixed in perpetuity. Instead, only donations made within a 10-year period play a role.
Further information: In Germany, one must consult - depending on where one lives - the tax authority of the respective state ("finanzämter"). The appropriate tax authority can be found via this umbrella site of the Bundeszentralamt für Steuern.
More information: Bundesministerium Finanzen
More information: Direction générale des Finances publiques
Other countries: Consult the local tax authorities.