https://tiekom.com/internet-at-home/data-sim/

The Sail Life YouTube channel brought this to my attention. This is 300GB with roaming for a monthly fee 43,90€. You don't need a home country contract. Speeds up to 150MB. 4G and 5G coverage
Sim card can be used in these countries:
Germany, Austria, Belgium, Bulgaria, French Caribbean, Cyprus, Croatia, Denmark, Slovakia, Slovenia, Estonia, USA, Finland, France, Gibraltar, Greece, Holland, Hungary, Ireland, Iceland, Italy, La Reunion, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Monaco, Norway, Poland, Portugal, United Kingdom of Great Britain, Czech Republic, Romania, San Marino, Spain, Sweden, Switzerland, Turkey. Azores, Guadeloupe and Saint Martin (French Caribbean), Guam, Guernsey, French Guiana (French Caribbean), Isle of Man, Mayotte Island, Aland Islands, Jersey, Kosovo, Madeira, Martinique (French Caribbean), US Virgin Islands, Vatican.