I had the same problem once, and writing the number without the dots solved it.
Here the steps I used to solved the problem. I choose the "WGS 84 / Pseudo-Mercator" CRS. This values does not exist in the Mercator projection, I choose it because I have no data about regarding the right CRS.
- save the numbers without the dots in a "CSV UTF-8 (Comma delimited) file. You can save any number of points that you need.
- Upload the file as "Delimited Text Layer".
- know you need to be sure that the X and Y fields are matching the latitude and longitude. Also, you need to choose the right CRS.
In your case "WGS 84 / Pseudo-Mercator" is not the right CRS, the point layer is nowhere to be found.
Know, you need to change the item CRS in the "layers" panel.
Inside this bar you can change the CRS and to see if you got the right CRRS. The red square should overlap the world map, which its CRS is "WGS 84 / Pseudo-Mercator".
Know, if you have any data about the location which that data was created you can try with CRS that related to a country. Historically, there are a lot of CRS that were used by many different countries, so you have a lot of options. If you don't have this info you can always go over the CRS one by one.