This is definitely one of those instances where you want to look for the official guidance and not ask random strangers on the internet. On the surface it's dead straightforward. You're a tax resident in Germany if you're living there for 183+ days a year. So the simple answer is only travel for six months or less. But it might me more complex than that in reality. In the UK for example you can technically qualify for tax residency even if you only spend 30 days per year in the UK, provided your only abode is in the UK and you spend those 30 days working. You can also notoriously live almost full time in the UK and work while still being non domiciled for tax purposes because the UK is the world's largest off shore banking and money laundering center and we like to make life easy for crooks and media barons. Speak to a tax law specialist. They'll be able to give you an answer in about 5 minutes.

Are you able to keep an "official" tax-address in Germany? That would be the easiest way while doing remote work.

You can take a look at digital nomad visas.

https://www.etiasvisa.com/etias-news/digital-nomad-visas-eu-...

I'd assume they are EU citizen so they don't need a visa, but tax residency is the bigger problem.

Can you claim an exemption for traveling for work? Maybe your ‘clients’ are really on the coast of France, in the Tyrol, or northern Sardinia.