I tried aegisub, but it was inconvenient: I can't control video playback with keyboard shortcuts and synchronization between subtitle sheet and video. It can be for any operating system (Windows, Linux, Android), except Apple's. I've seen some apps (seems to be free), but I don't know if they can be trusted/good.
You can try https://nikse.dk/SubtitleEdit/ .
Subtitle Edit is a free (open source) editor for video subtitles - a subtitle editor :)
With SE you can easily adjust a subtitle if it is out of sync with the video in several different ways. You can also use SE for making new subtitles from scratch (do use the time-line/waveform/spectrogram) or translating subtitles.