[mntmoss]

In two parts:

1. Fix the underlying ergonomics. Put your monitor higher and your keyboard closer. The position you want is like the rest position of a dancer: elbows nearly against your sides, relaxed. (Taking an actual dance class will teach a lot about posture habits). A small change of a few degrees here and there can make a big difference. If you are a laptop user and have been actually resting it on your lap, try putting a shoebox or similarly sized object under it.

2. Train mobility. The hunch develops as a result of persistent overtraining in one direction. You don't need a lot of additional strength to start to correct this, just mobility.

Look up Youtube channel "Calisthenic Movement" - there are some very good mobility routines and I have incorporated parts of them into my everyday workout. Some of them use a pull-up bar but most are pure bodyweight and the floor or a wall.

If you want to stock a home gym I suggest going for resistance bands - they're small, light, cheap, more forgiving than weights and hugely versatile.

[Symbiote]

A laptop user should either buy an appropriate stand (I have [1]) and keyboard and mouse, or a monitor. Or both.

This is so essential to a reasonable posture that it's essentially required by workplace safety regulations in Europe. (In other words, in Europe your employer should buy these things, including for working at home.)

[1] https://www.therooststand.com/