Moving from WhatsApp to Signal is an important action, right now. WhatsApp’s parent company, Meta, has been involved in several cases of election interference: America in 2016, Trinidad and Tobago …
I will use the opportunity to remind that Signal is operated by a non-profit in the jurisdiction called "the US". This could have implications.
A somewhat more anarchist option might be TOX. There is no single client, TOX is a protocol, you can choose from half a dozen clients. I personally use qTox.
Upside: no phone number required. No questions asked.
Downside: no servers to store and forward messages. You can talk if both parties are online.
You can use Signal with a different client. Signal being operated within the US has no effect. As of now the jurisdictions that I know of to be worried about are:
The White House both in Trump's first term and in Biden's presidency were pro-encryption. Signal and Tor were US government funded projects. That's not to say the US is great on encryption, and there have been laws in the past that did/were proposed to limit it. But, as of now, it seems that the US is (edit: one of) the most hospitable jurisdictions for encrypted messaging non-profits.
BTW, I'm not saying using Tox is bad, or that Signal is good, I'm just talking about the US jurisdiction part.
Can you advise, which one would be a good one? Because I actually use Signal too, it's just misbehaving a lot recently.
I have had endless difficulties with Signal forcing upgrades on me and requiring to sign in on the phone, under threat of deactivating my account (I use it on a PC).