I beleive anybody interested in computing should at least once, contribute to open source projects. In particular the ones licensed with Free Software licenses that respect the four software freedoms. Below are some of latest ones I have contributed to this year 2021.

Project License Repository
Webtrees GPLv3 code
Zoneminder GPLv2 code
Pixelfed AGPLv3 code
Privacy guides CC0-1.0 code
doctoc-docker Apache-2.0 code
Big Blue Button LGPLv3 code
Awesome Privacy CC0-1.0 code
Reuse tool GPLv3 code
www.darktable.org.es AGPLv3 code
www.darktable.org CC BY-NC-SAv3 code
darktable GPLv3 code
Exiv2 GPLv2 code
Peertube AGPLv3 code
Lensfun LGPLv3 code
linuxserver GPLv3 code
Mercury Cryptocurrency arbitrage trader AGPLv3 code
FSFE Website AGPLv3 code
FSFE CD Front AGPLv3 code
FSFE PMPC CC BY-SAv4 code
OpenStreetMap ODbL code
interBTC and Kintsugi docs Apache-2.0 code
interBTC Clients Apache-2.0 code
interBTC API Apache-2.0 code