Shraddha anukalpas(alternatives) given by our Dharmashastras, to address the practical difficulties of people. Dharmashastras allows 7 different ways in which Shraddha can be performed.

KshaNa
Kurcha
Aama
TarpaNa
Hema
Gograasa
Namaskara

....Shraddhas https://twitter.com/pranasutra/status/1330030559880486921

Kshana Shraddha ...Minimum of two Vipras (learned in at least one Veda), Brahmins, and cooked food required. If such Brahmins r not available, then at least ones knowledgeable in Purusha Sukta, if such ones are also not available then those knowledgeable in Gayatri mantra.

Kurcha Shraddha ..If Vipras knowing Vedas, Purusha Sukta & Gayatri r also not available, then use Kurcha(Dharba grass), to represent Brahmins(in whom Vishve devatas & Pitru devata r invoked & complete the Shraddha. This Shraddha also requires cooked food to be offered to Pitrus.

Aama Shraddha ...If one does not have facility(Agni/fire) to cook food also, then Kartru can offer uncooked food to the Brahmins and complete the Shraddha. Raw vegetables, rice etc etc.

Tarpana Shraddha or Sankalpa Shraadha ......If one can't find raw uncooked food too, then one can complete the Shraddha by just offering Tarpana of Tilodaka to the Pitrus. Tarpana is also a compulsory ritual in Kshana, Kurcha, and Aama Shraddhas.

Hema Shraddha .....If the Kartru is in such a situation that he can not even do Sankalpa Shraadha, then one can give Hema(Gold, physical money, digital money nowadays) to the Brahmins and complete the Shraaddha.

Gograasa Shraddha ....If the Kartru does not have money/gold, dhanyas(grains) required to perform Shraddha due to poverty , then he can cut grass, he can find in the fields and offer it to the Cows. By just offering food to the Cows, one completes Shraddha ritual.

Namaskara Shraddha ...If one can't even provide food to the cows, then the Kartru can lift his hands towards the sky & express his helplessness in conducting Shraddha by any other means, & offer Namaskaras to the pitrus to satisfy them. So a mere Namaskars will complete Shraddha.

Source of all the above information pravachana of Dr Satyanarayachar principal of Poorna Prajna Vidyapeetha, Bengaluru. Watch from 11 minutes onwards to about 37 minutes. to pujya Acharya.