HK 24/4 - ferry on 26/4 from shekou to Macau

Actually, the only way to enjoy 144 hour visa free transit in Guangdong province, Shenzhen included, is to fly from Hong Kong to Guangzhou and to return, as you have written, by ferry from Shekou port in Shenzhen to Macau. The rule is clear on this matter because only the entries by air are considered eligible for any visa free transit option in Guangdong province.

Your, probably more convenient alternative, if you go to Shenzhen only, is to apply for a 5 day Shenzhen visa on arrival. In other words, you can obtain a visa at Luohu (Lo Wu) border crossing valid for 5 days at the price of 168 CNY. After your stay in Shenzhen, you can return directly to Hong Kong using any border crossing or any mean of transport including a high speed train. Please, have in mind that visa office is open until 16:30 and you will have to bring a negative PCR or antigen test, not older than 48 hours at the time of your arrival at the border crossing.