which martial art to learn?

Whichever is most available to you. Change arts often (give them at least three months, preferably a year.) Get into each their own styles and cultures. Each offers something worth learning, even if only as a contrast to other systems.

What is your purpose?

Kick boxing to kick anyone’s ass

Boxing for good sportsmanship and how to throw a proper punch.

Wing Chung for the little guy who wants to stand up to anyone.

MMA if you’re ~25, peak fit, and want to be a tough bad ass.

Capoeira for a great full body fitness and all round physical confidence.

Any of the traditional styles if you’re also interested in a drastic lifestyle change.

Start with fitness, work on form and technique, and find something that really suits you (and keep at it!)

Boxing is the only art which teaches you how to hit from the start. Most others will have you doing forms and basic exercises for the first year (or more!)

Any traditional Japanese martial art (ko-ryu, existing before 1868). Martial arts which date at least that far back existed in a feudal era where the skills taught were actually used. Japan is rather unique in that time period is almost within living memory.

I would've answered the question on the tech downturn but now refreshing the page (to see if anybody else answered in the meantime) it's about martial arts. https://imgur.com/a/vTZjrxB This makes me not invest time to answer thoughful questions from this user again.