If there is no problem with English, try to choose XML. As you said, there are few jobs on mainframes. Of course, it is undeniable that the salary of mainframe in the same position is much higher than that of XML, because not many people can pass the certification. General enterprises need talents in this field to work directly, and are unwilling to pay a high price to invite a semi-finished engineer back. But from the current situation, some companies should be one in a hundred in this field. Although not many people pass, even if they pass, it does not mean that they are recognized by the company. However, XML is different. Although it is basic and low in technology, the entry threshold is low and there are many starting points for work. In this way, on the one hand, you can master your skills at work, and on the other hand, there are many opportunities for promotion.

Supplementary answer:

It is really tempting to say that there is a reward for giving. But as far as the current global economic situation is concerned, the best job seekers are those with advanced knowledge and proficient skills. Maybe you only saw the gold content of the examination certificate, but didn't pay attention to the needs of many companies at present. From the perspective of empathy, many companies need work experience when choosing talents. Especially the mainframe, a subject with a small range of options, is not used by small companies. Generally speaking, large companies have their fixed range of choices. If you are the human resources minister of the company, do you choose a novice postdoctoral fellow or a junior college student who has worked in the post for 10 years and won numerous honors? Most people don't worry about the distance of study. Since we have this goal, we may have perseverance in the end, but we must consider it when we take office. I'm afraid we'll have to start with a junior position and a position that doesn't involve mainframe knowledge. Think about whether you want to have a taste. Think of a rap lyric: I studied arithmetic for 10 years, but finally let me feed the pigs.

I think it is better to choose to enter the door of any company, and the knowledge that can be used immediately and helpful to any position is better.