Welcome to the forum. Using your thumb to depress the follower button on a Luger mag will quickly give you a sore thumb. The Germans made a combination tool that also serves as a loading assist to make it easier to put a full 8 rounds in a Luger mag. As already mentioned, Mec-Gar mags have strong springs so a tool is almost necessary.
Original tools are expensive but there are reproductions on ebay and also sold by Sarco and Numrich as well as other places. The repros that I have all work well.
https://www.gunpartscorp.com/products/466170
https://www.sarcoinc.com/luger-tool-with-early-marking/