No one really knows at this stage (including the government themselves) what will actually happen.
There might not be any increase in the minimum requirement at all, it might be a much smaller increase to just £26,000 and any increase might not be applied retrospectively to people applying for extensions and ILR.
The government has specifically admitted that they do not know if any increase will be applied retrospectively, it's something that they have not yet decided on but will come to at some point.
I would say however for your specific situation, that if there is an increase to £38,700 AND it is applied retrospectively to effect ILR applications that it would be highly unlikely to effect you if you will be applying for ILR in March. The government has stated that any changes will come into place in 'Spring' 2024, and I would assume that would mean from April and on.
But we still have a very long way to go, this current government is a complete shambles and I would be extremely surprised if everything is actually in place to enact any changes by April.