How to use different fonts for two lines within the same cell in Excel?

I have an excel file with a table A6:E233. I had to concatenate columns A and B so that values from B are displayed in a new line. I have achieved that with the CONCATENATE function (and CHAR(10) for new line) that is built into Excel.

After concatenation the spreadsheets looks like this:

EXAMPLE1

Now i would also need different formatting for each line inside the cell, namely size 12, bold for the first line and size 8 for second line:

EXAMPLE2

How do achieve this? If it would be a short table, I would do it manually, but since I have a few files, totally well over 5000 rows, maybe an automated way would be better.

I have found answers that touch upon this problem, but since I dont know how to use VBA, I am more or less lost. I am also using a lot of python and have looked through openpyexl and csv, but have not found a way how to achieve this.

Thank you for your help!